Here are some good free sans-serif fonts that have popped up over the past couple of months.
Gandhi Sans is a great looking humanist sans-serif similar to Gill Sans. It comes in the four standard weights of regular, italic, bold and bold italic, making it very useful for standard Word processing. There is also a matching Gandhi Serif, the combination of the two is similar to Gill Sans and Perpetua.
Karla is a great looking open humanist sans-serif in the Swiss style, but with a bit of personality in the double storey g and wonky q. Karla is available in regular, italic, bold and bold italic.
Oswald is a condensed bold humanist sans-serif, good for headlines and similar to Franklin Gothic Condensed.
Economica is a condensed geometric sans-serif with chamfered terminals and could be used as a display face for technology and SciFi. Economica is available in regular, italic, bold and bold italic.
Titan One is a big friendly looking heavy humanist sans-serif. It gives the impression of comics and brush strokes.