TechCrunch recently launched an online Web 2.0 dictionary site (go2web20.net).  It is fantastic.  I highly recommend checking it out.  For those in education you can click on the ‘Select Tag’ at the top and select collaboration below that (sorry no direct link).  It has some old time favorites, but there are a lot of new web applications I have never seen before. 

Note:  They are constantly updating the list too.  Since yesterday there are already two new applications.  Looking for something new to try out… great place to start!