There are too many theories of self within the tradition of Western psychology to count them all. To my knowledge, no one has ever attempted to cover them all in one place and at one time; the task would be enormous, not to mention time consuming. For these reasons, I do not endeavor to be the first to attempt this task. Instead, I will attempt to present an overall view of the self in Western psychology that incorporates the most prevalent and commonly used theories.
In general, the goal of Western psychotherapy (particularly when rooted in the psychodynamic tradition) is to strengthen the self in order to improve functioning, facilitate healthy regulation of emotions, and increase ability to cope with both internal and external stressors. Most Western theories of psychological development assert that "the self" develops through a series of hierarchical stages, with each new stage representing a higher level of self achievement than the one before it.
An infant begins its life with no sense of himself as an individual separate from his external environment. The infant embarks on his self-developmental journey in the context of his relationship with his mother (or primary caregiver). The infant is dependent on his mother for all of his basic needs. He has only to cry and his mother is there to provide what he lacks. For this reason, he comes to see his mother as an extension of himself; he perceives an entity he calls "me and mommy" that is separate and distinct from the rest of the world. As a young toddler, the child begins to recognize that he is his own entity, existing in his own body, separate from everything and everyone, including his mother. He begins to try to manipulate objects and interact with people in his environment. Eventually, as he becomes more confident, he begins to venture farther and farther away from his mother and for increasingly longer periods of time. As the child gains a growing sense of himself as an individual separate from other individuals, he gradually becomes aware that his actions affect others. He develops the ability to feel guilty when he does something that hurts another person.
Each stage of the developmental process must be navigated successfully in order for a child to eventually form an integrated personality and a healthy sense of self. The successful resolution of each stage endows the ego with a specific ability or "virtue" that contributes to healthy functioning. While development continues throughout the life span, the years from birth to adolescence have the most significant impact on personality development. If all goes well, an adolescent will enter young adulthood with the ego strengths of hope, willpower, purpose, competence, fidelity, and love.
The culmination of psychological development is a differentiated self. When a person is differentiated, he is able to function as an autonomous individual with his own ideas, opinions, goals, and pursuits. He is capable of maintaining healthy boundaries with his family and friends; he is neither controlled by nor enmeshed with others, nor is he emotionally cut off or disconnected from them. He has the capacity for emotional intimacy. A well differentiated individual can separate thoughts from feelings. He is able to regulate his emotions such that they do not overwhelm his ability to think rationally.
While the self gradually develops into a separate and independent entity, it does so only in the context of one's relationships with others. I am aware of no theory that conceives of the self as developing in a vacuum; there is widespread recognition that the self develops in (and is therefore influenced by) a broader cultural and interpersonal context. I am also unaware of any theories suggesting that the self emerges fully formed. Rather, the self is always seen as something that must be developed over time; it requires specific things in order to do this successfully.
In terms of how self is defined in Western psychology, most schools of thought recognize at least two "realms" of the self: the conscious and the unconscious. Not every school of Western psychological thought attends to the unconscious aspect. Behaviorism, for example, focuses on changing overt behaviors without addressing the possible unconscious factors that drive them. Other theoretical orientations address the unconscious factors in mental illness indirectly. For example, cognitive theory focuses on changing irrational automatic thoughts, rules/assumptions/schema, and core beliefs. Automatic thoughts tend to reside just below the surface of conscious awareness and can usually be accessed pretty easily. Schema, followed by core beliefs, occupy increasingly unconscious levels, which are less accessible to conscious awareness. For this reason, the presence of certain schema and core beliefs is typically inferred from associated automatic thoughts and emotional triggers.
While we are not, by definition, aware of the contents of the unconscious mind, the unconscious nevertheless has a significant influence on our thoughts, feelings, and behaviors.
At the center of the conscious realm of the self lies the ego. The ego serves many purposes and is vital to healthy and adaptive functioning. Among other things, the ego acts as a gatekeeper between the conscious and the unconscious. The ego determines, based on a number of factors, what material is allowed into our conscious awareness and what material is to remain unconscious (and probably, to a lesser degree, what information is to be discarded completely). The ego is also responsible for organizing the personality so that it is coherent and consistent. It is essentially responsible for creating our "sense of self."
The true self consists of both the conscious and the unconscious. To experience the true self, a person must integrate his conscious and unconscious minds. This requires becoming aware of the material hidden in the unconscious mind. This material is often difficult, aversive, and anxiety provoking (which is why the ego has not allowed it into conscious awareness). Becoming aware of this material also means dealing with (and tolerating) the negative emotions associated with it. This is a difficult process, but one that promises very desirable payoffs. To experience the true self is to expand one's consciousness and to more fully know oneself. A perosn's thoughts, feelings, and behaviors are controlled by unconscious material so long as that material remains unconscious. To become conscious of this material is to begin to gain control of it (and to therefore gain greater control of one's thoughts, feelings, and behaviors).
Despite its many necessary functions, the ego can hinder one's quest to experience his true self. Recall that one of the roles of the ego is to act as the gatekeeper between consciousness and unconsciousness. Thus the ego can, at times, interfere with efforts to know the true self by preventing unconscious material from entering conscious awareness.
Essentially, the basic premise of Western psychotherapy is that a fully developed "self" is necessary for healthy psychological and emotional functioning. The inability to regulate emotions, to cope with and tolerate distress, or to maintain intimate interpersonal relatinoships with appropriate boundaries are all recognized as symptoms of a poorly developed self. Perfectionism, anxiety, compulsiveness, self-destructive behaviors, or rigid beliefs are also manifestations of an underdeveloped self. Thus, the goal of Western psychotherapy is to build and strengthen the self, which in turn leads to an alleviation of symptoms and improved overall functioning.
It seems to me that modern Western psychology does not take an ontological stance in its conceptualizations of the self. In this context, I use the term ontological to refer to "the philosophical study of the nature of being, existence, or reality." (I'll admit it - I just quoted from Wikipedia). Ontology deals with such questions as "What does it mean to exist?" "When does something cease to exist as opposed to simply changing?" (What if a person sustains brain damage? His personality is not the same as it was before the damage occurred. Is he still the same person)? "What makes up the identity of a person or object?"
These questions have been contemplated by countless Western psychologists and psychiatrists over the years. Some have taken a philosophical approach and have generated theories based upon ideas emerging from their own intellectual thought. Others have formed theories generated from their observations of and interactions with patients. Still others have taken a more spiritual approach, drawing from the teachings of various religious and spiritual traditions and combining them with traditional psychological theories.
Western psychology has always struggled to be taken seriously as a "hard" scientific discipline. In order to assert its legitimacy as more than just a pseudo-science, it has adopted increasingly rigorous standards for ideas, information, and practices it is willing to accept as valid. As a whole, psychology and psychiatry are no longer willing to accept or endorse anything that has not been studied empirically via controlled scientific studies. (There is, of course, significant variation among individual practitioners in their willingness to engage in psychotherapy practices that have not been empirically validated).
Because of this, the field appears to be moving towards an embrace of an almost reductionist coneption of the self. This is increasingly the case as new technologies are developed that enable researchers to study directly the activities of the brain. The neurological underpinnings of phenomena that have traditionally been ascribed to the self (e.g., thoughts, feelings, perceptions) are being identified and explored by researchers via sophisticated brain imaging techniques. Because these phenomena can be observed on a neurological level, there is a broad assumption that all human experience is simply a result of the various physiological functions of our brains and bodies. To me, this conclusion seems to ignore one of the basic principles of the scientific method: correlation does not equal causation. It also assumes that everything that exists can be observed directly and demonstrated objectively. There are, of course, other ways of knowing; its just that Western society as a whole tends to reject anything they cannot prove.