I love GitHub. It's Network Graph Visualizer is outstanding! It solves one of the biggest challenges in open-source world; keeping track of what other people have done with the code base.
If you use Windows for writing your code you can use the tools described here to have Git on shell context-menu. For Visual Studio support you can use GitExtensions and/or Joshua Flanagan's GitMacros. The last one requires you to do some steps for adding the macros manually but it's worth it, since you can have some basic GitHub functionality in minutes (like opening the GitHub page for the current file).