Earlier I posted about an informative video detailing what Web 2.0 is and what it means. Here's another view: This wonderful graphic comes from Harold Jarche via Steve Dembo. By the way, Steve did an informal poll asking fellow bloggers what their top three Web 2.0 sites. Which one came out on top? You'll have to read his post to find out.
For the record, the three that I find the most useful (as of right now) for what I do as a teacher:
-Wikispaces - free premium site for educators. Great interface, awesome tech support, and easy to incorporate various applications and elements. Don't believe me? See for yourself.
-Google - I can't just pick one, but for direct impact on teaching it's Google calendar, which has student due dates and my planning calendar. I think I've mentioned these guys in the past.
-Bloglines - Just beginning to appreciate it for the way it allows me to read numerous blogs (see blogroll to the right). Plus, I just began using it to easily keep track of what my students are posting in the wiki project (see #1).