Droid Fonts
With the advent of the Android operating system for mobile devices, which was eventually purchased by Google, a family of fonts known as Droid was commissioned.
Pretty, easy to read, and free!
AScender Corporation’s Steve Matteson began work on them in late 2006, and my do they look nice. Although the OpenType versions (with ligatures, glyphs, and other obscure characters) cost $30 each, you can get the bog-standard TrueType ones (released under the Apache License) from here at Android’s git repository.