Since I have tried Ubuntu font I haven't used any other on my e-ink reader.
I tried many fonts and some of them were very nice for reading, such as Gentium, Droid, liberation sans.
http://font.ubuntu.com/
Also have a look at google fonts for a high quality fonts you do not ahve to pay for. You can download the font even if Google tries to persuade you not to - most people want to use them for their web pages and they really do not need to download, just link to them.
https://www.google.com/fonts