Recently I have discovered Ubuntu Font Family
http://font.ubuntu.com/
At first I was afraid that it is too minimalistic. Relatively large x-height, "crossings" on letters 't' and 'f' are very unusual, 'r' looks weird. But, the result is very, very nice. In FAQ they say that "extensive manual hinting was performed" and I think it shows.
Great font. And free. And it comes in four weights - Light, Regular, Medium and Bold, in Normal and Italics
