LUGAL BibDesk is absolutely wonderful software, far better than any other BibTex manager I've ever used. I've been using BibDesk heavily for a few years (writing my dissertation), and the only problem that I've ever had was fixed by the developers on the same day that I reported it.
It's a deep program, with lots of features that I don't use, so it might seem a little overwhelming to the uninitiated, but it's so good that anyone who needs to manage a large bibliography--even if they don't use BibTex--really should try it out.
(Version 1.3.13)