The font that you choose has to be installed on the viewers' systems in order for them to see it. Realistically, this means that you can really only specify a few typefaces — the ones you are fairly certain will be on the viewer's computer. This can be confusing, because you'll see the fonts on your computer, but others won't see them on theirs.
You'd think that choosing fonts common to Windows would be safe enough, but then there's the MAC to consider...
Check this page out click here for fonts that are common to both Windows and Mac.
I use Tahoma or Verdana for body text. Both are sans-serif fonts, considered easier to read in a browser.