Just thought I'd update briefly on my own thoughts.
It's just not possible to get exceptionally crisp text that approaches what you get in print. I guess that is one aspect of the e-readers that I will hope for improvements in in the future. So rather than obsessing over that detail, which is inherently limited, I decided to re-assess my priorities in typeface experimentation to what will produce good readable body text.
There are a few fonts that I have and have been using that I consider my favorites not necessarily because of their perfect clarity, but because they are very easy to read as body text. Those two are Chaparral Pro (I like size 10.5) and Arno Pro Caption (size 10). Avance is also pretty readable at small sizes (10 and under), and there are some others I've been meaning to try out (like Museo), but I haven't spent the time yet. There are also numerous typefaces I don't have that I'd like to try (The Antiqua, Meta Serif, Milo Serif).
Actually, between Arno Pro Caption 10pt and Chaparral Pro 10.5pt, I'm pretty satisfied!
However, for those who don't have those options,
Gentium Book Basic is free, and does a pretty nice job overall. If I didn't have the commercial fonts, it would be one of my first picks.
Grandesign Neue Serif is also free and good, but I think it's just a wee bit dense (while clear, it might not be the most readable for body text). I've been meaning to try out
Museo but haven't had the chance.
Fontin, as some recommend, isn't bad but not my cup of tea...but it's free so it's always worth a shot. A cursory search for free slab-serif yields a few possible interesting options, but nothing that really strikes my personal aesthetic fancy.