Webapps are pretty awesome, even if they are a little slow.
Here are some of the best.
1. Google Calendar
Probably the best calendar application out there.
2. ZoHo Office Suite
A fully functional office alternative, online.
3. Aviary's Phoenix
Almost everything you'd expect in an Image editor. Plus, Aviary seems to be coming out with a heck of a lot more awesome apps.
Online video editing and retouching.
Chat using GTalk, Yahoo!, AIM, and MSN.