I thought it could be handy to have a fonts-thread to point out (free) fonts that work well on the Kobo.
To receive a good result in most cases one should put at least the 4 most used styles of a font-family into kobo's fonts-folder, they will be detected and listed as 1 font in the selection-menu and handled accordingly. The 4 basic styles are Regular (or Roman), Italic, Bold and BoldItalic.
As I find
Caecilia (the standard Kindle-Font) quite convincing, I had a look for similar Slab Serif Fonts and found
Charis SIL:
http://www.fontsquirrel.com/fonts/Charis-SIL
Android 4 ICS introduced a newly created sans-serif-font,
Roboto, that is especially fit to deliver good readibility in very small letters and look still nice as a heading etc. If I want more / smaller text on each page I prefer Roboto over the others, it really does, as it is supposed to, look still easy and "spacey" (as opposed to "overcrowded") in smaller font-settings.
http://www.fontsquirrel.com/fonts/roboto
While comparing the Android-Fonts Droid Sans (Android 3) and Roboto I found
Droid Serif, that is nice in small sizes, too, and adds a screen-optimized serif-font to this collection.
http://www.fontsquirrel.com/fonts/Droid-Serif
Which fonts do you use and like (and why?)