Linux Libertine works well and looks good on the sony. Its a very professional font.
http://www.fontsquirrel.com/fonts/Linux-Libertine
Are you sure you want to post a copyright book here JSWolf?
Another cool epub feature: if the font size is set to be read in "medium zoom" on the sony in portrait, the font appears at exactly the same size at "small zoom" in landscape mode.
Reflow FTW!
(btw this is not the case with LRF files)