Mendeley

If you're having trouble managing your bibliographies and paper / literature collections, you should try out Mendeley, probably one of the most integrated and comprehensive digital library management systems out there. Not only does it support importing citations from PubMed, ACM, etc. a la JabRef, but it also synchronizes with CiteULike. Moreover it allows synchronization across machines, sharing of libraries with other users, anywhere-access, literature trend tracking, and other such goodies. And a pretty slick interface - as icing on the cake. It appears to me, more robust and comprehensive than JabRef (which is quite excellent but unfortunately restricted to your local machine).