BookBurro notices that you’re looking at a particular book and searches the web and local libraries for it. Very handy if, like me, you bounce between amazon, powell’s, abe and half.com before you buy anything.

Zotero pulls in reference data on books, articles, and websites as you view them. It also lets you sort and add tags. The bib info function was the big draw for me, but it also does a number of other things I need to explore. (After exams!)