I have several favorites, but readability has a lot to do with the medium. On screen readability is not the same as printed by any means. For printed media in large blocks of text, I suggest Baskerville or Garamond. Large bodies of text should be in a serif font.

I would rank the top 10 fonts for printed text (large bodies of text) this way (favorite to least favorite).
1. Garamond
2. Baskerville (or New Baskerville)
3. Book Antiqua
4. Georgia
5. Goudy Old Style
6. Acanthus
7. Caslon
8. Atlantix
9. Bauer Bodni
10. Century Schoolbook

For titles or fancy text I would say go with:
1. Bernhard Modern
2. DeVinne
3. Tiffany

For a sans serif you can't go wrong with Arial, but Swiss is also really nice.

In a pinch, for a serif font, Dutch is also good. I tend to avoid CG Times, Times and Times New Roman if I can, because it is just WAY over used (my opinion), plus I do not find it that easy to read. I have much less eye fatigue reading Garamond or Baskerville.