Web-based Applications (+Edit)
Here are two lists of web-based, no-install applications worth perusing and trying:
From the netHACKZ website, 15 Killer Web Apps That’ll Rock Your World, and from the SmashingApps website, 21 Online Free Web Based Applications That You Probably Would Love To Use Every Day!
Web-based applications are a double-edged sword of sorts. They are platform-independent which makes them good for users of multiple computers and/or non-Microsoft operating systems. They do require internet access, which makes it tough to be productive while offline.
There are still worth a look, in our humble opinion…
Edit 10/18/2008:
A recent post on The Emma Alvarez Site lists 55 Recommended Free Online Tools.