Arial & Tahoma.
I've used Georgia too.
Unless you are doing them in a list (Tahoma, Georgia, Arial) then you
should be prepared for many of your clients getting their own default
(Times Roman on most systems, Helvetica/Arial on a few).
If you want a more interesting font, it generally has to be reserved
for use in titles as a drawn graphic. Then you have to compromise on
the body font to something that's close(thereby violating a major
graphic design rule - but you don't get much choice on web pages and
compromise is required).
