Here are some font resources you should be aware of:
Source Sans Pro
Source Sans Pro is Adobe's first "open-source" type family. The free sans serif type family is available in 12 styles, and includes a number of OpenType features such as fractions, old style numerals, and stylistic sets. As an open-source typeface, it is completely free to use for any private or commercial purposes. You can read more about the development of Source Sans Pro here.
Source Code Pro
Google Web fonts
Google Web fonts is a directory of "hundreds of free open-source fonts optimized for the web". However, as my friend Bob Levine pointed out recently, the fonts can also be downloaded in TrueType format for use in print or digital projects. To do so,
1. Visit www.google.com/webfonts, browse the fonts, and add one or more fonts to your collection.
2. Click the Download your Collection link in the upper-right corner of the Web page.
3. Follow the on-screen instructions to download the fonts in your collection as a zip file. You can then unzip the file and install the TrueType fonts on your system.
Source Sans Pro, Source Code Pro, and all the Google Web fonts are all licensed using the SIL Open Font License.