The theme that stands out most prominently is the search to recapture lost innocence. For example, Holden uses a kind of illogical spontaneity to try to recapture innocence when he makes a spur-of-the-moment proposal to run away with Sally Hayes. Sally's dismissal of Holden's idea reinforces his outsider status again and brings Holden squarely back to the present, one in which he does not feel young and innocent.
Another omnipresent theme is that one can use failure to become the center of attention. Holden continually sets himself up for failure. He fails in every encounter with other people. For Holden, failure serves as a great attention-getting device. And perhaps, more than anything, Holden wants attention from his parents, the absent characters in the book.
A third theme I'd like to mention is that of authority figures not being trusted or respected. Most of Holden's interactions with authority are marred by some kind of discomfort, ignorance, or unawareness on the part of the adult. But, perhaps the best validation of Holden's suspicion toward authority figures comes toward the end of the novel when he stays over with his former English teacher. Mr. Antolini gives Holden sound and intelligent advice about getting his life back on track. However, Holden soon discovers he cannot even trust Mr. Antolini. Holden awakes in the night to the English teacher inappropriately stroking his hair.
There are other themes, however, these three stand out to me most prominent.