I think verdana, helvetica and Times Roman are the most common.

Also, here's a helpful font usability study from the University of Wichita [psychology.wichita.edu]. In fact, their psychology dept has several practical web usability studies online.

Personally I like Verdana or Tahoma

That seems to be a general user preference - in general people prefer sans-serif fonts. The problem with serif fonts is that they "fight against" the square block nature of screen pixels. Verdana was intentionally created to minimize that.

Here are a few more articles about Web type:

[typographer.com...]