The quality of available free fonts has increased dramatically in the last few years. As Jeremiah Shoaf said in his recent article on smashingmagazine.com:
Here are a collection of a three great free typefaces we have recently found that you can download and add to your collection.
Alegreya Sans by Juan Pablo del Peral
Alegreya Sans is a san serif family that has a feeling of calligraphy stokes. It is a very versatile family that can be used in large and small sizes, for both print material as well as for a web font. It has loose, even spacing and short serifs.
Ostrich Sans by Tyler Finck
Ostrich Sans is a slender, clean typestyle. The entire family is essentially condensed with mathematical corner calculations on the bowls and arcs. It is a great choice for headlines and is available in a range of eight free styles.
Exo by Natanael Gama
Exo is a contemporary geometric san serif typeface with a technological feel. It performs well in small, medium and large sizes and comes in a great range of 9 weights.