Are you a student, researcher, or information hog? Then you should check out Zotero.
I have been using Zotero about six months now and it is probably the single best reference management software I have ever tried – and I have tried (and paid for) all the big ones (ProCite, RefMan, EndNote). Not only is Zotero free, it’s better. Seriously.
And considering the downright nasty lawsuit by Thompson-Reuters against the makers of Zotero, I regret ever having paid the big bucks for their comparatively lousy products.