The easiest thing to do is to add a file to your Kindle. A blank file called USE_ALT_FONTS. put it in the top level of the kindle directory. Eject and restart the Kindle. You will then see all the hidden fonts that are already on the Kindle. I found one that I love, so no need to add new ones. I learned about it here
and he links to a thread here on mobilread where he found it. (I did step 3 & 4 but then removed that font folder, as the ones that showed up were fine for me).
Oh I see the link above provides the same info....anyhow there is a nice screen shot on the link I provided.