Octarine light and bold versions are free. The remainder of the styles of this beautiful font can be had for a minimal fee.
You can download Fivo Sans here—absolutely free for personal and commercial use.
You’ll notice at the bottom of the page below the download link that the author of the font also offers Fivo Modern, a great variant of Fivo Sans, for free. Donations for both fonts are welcome.
I love a nice, clean, well-rounded sans-serif font! Gilroy is kind of a cross between Gill Sans and Avenir; two fantastically readable fonts that work large or small.
Gilroy is a full family of 20 fonts which you can get for $45. But you can grab the Light and Extra Bold versions for free. Download the Gilroy freebies here.
Junction is a free humanist sans-serif, and the first open-source type project started by The League of Moveable Type..