The personal learning network for educators
Too many to fit on a wall!
I like Wallwisher and often use it with my classes.
There are many sources of favourites on the web - for example, Jane Hart's Top 100 Tools for Learning. I posted a link here together with some of my own personal favourites. Note her list for the classroom.
Diigo has groups where people share links to web 2.0 tools also, see these for example. In fact I find that belonging to a few of these means there is quite a lot of duplication as people post the same link to several groups.
See also the links here which I provided for staff at my school. (The Diigo list includes sites with much information).