Source Sans - from Adobe

Typefaces with multiple weights are really useful for adding dynamism to any project involving type. A free font that fits this description admirably is Source Sans from Adobe.

Source Sans Pro was designed by Paul D. Hunt as Adobe’s first open source typeface family, conceived primarily as a typeface for user interfaces. Source Sans Pro draws inspiration from the clarity and legibility of twentieth-century American gothic typeface designs. it is available here in 12 weights, from extra-light to black