I am wondering if anyone has tried Minion Pro on their ereaders? It comes in both medium and semi-bold weight, I think one of those might work well. For those who like sans serif, Myriad Pro is very nice, I use it a lot for documentation in my job (but I personally don't like reading with a sans serif font).
I did try out Amasis Modified and I found it be a little bit blocky for my taste, too uniform in weight. I guess I like more traditional serif fonts.