I'm probably the last person to know about this but a colleague just tipped me off about Zotero. It's a bibliographic database add on for Mozilla Firefox.
It is FREE!
And it is utterly, amazingly BRILLIANT!
None of the faffing about downloading marked lists etc as on Endnote and Reference Manager...
You just click on the little icon that comes up in the URL bar (a file/book for a single item or a folder for a list of items) when you're - for example - in Amazon, or your library catalouge, or an electronic bibliographic listing - and it automatically downloads the citation information into your database.
Very intuitive to use (a bit like iTunes). Lots of facility to download different output styles and to cite while you write etc...
I can't believe I managed without it.
Just thought I'd share that with you