The Droid family from Ascender, which Google commissioned for Android is uniformly excellent, renders well everywhere I've seen it and is Apache Licensed. I'm currently using 'Droid Sans' as a system UI font (on Linux) and 'Droid Sans Mono' for coding, terminals, etc... In fact I've just aliased the linux 'sans', 'mono', etc... to the appropriate Droid face.
I think Droid and Liberation are siblings, from the same designer & foundry. Liberation has more variations (italic, bold italic) and more "flourishes" (like in the uppercase Q, lowercase a and what not).
More info here, including the link to the git repo if you want to check the fonts out: http://en.wikipedia.org/wiki/Droid_fonts
these are in the Ubuntu repo's as 'ttf-droid' or you can do a straight download from here:
http://damieng.com/blog/2007/11/14/droid-font-family-courtes...