Of course this goes the same with the sources tarballs. SourceForge and Free(Code) are good to start with as they often show statistics, reviews, etc of the apps. I prefer to download the source tarballs from the developer's site if available - quite often in git or subversion. There are md5sum that go with the tarballs, check those as well.
Other sources for me include, Github and Gitorious.
I'm gonna be quiet about something ... for a change. Thanks, Tex!