Seriously, Github. You can scroll through popular projects, or filter some language that you are interested in and just see those projects. Most of the good projects have a section in their README about Contributing, which helps guide newcomers with details on how to start contribution code to the project. It really depends on what your interests are.
For example, say you are interested in collectible card games, you could decide to contribute to a project that manages a person's inventory of cards. So you end up doing a search:
https://github.com/search?utf8=%E2%9C%93&q=card+inventory&type=Repositories&ref=searchresults
Looking at those projects they seem to be in their beginning stages too. There were at least three of them that had less than 20 commits when I looked. I also noticed that each project only had one author posting commits. So... probably not the best selection if you wanted to join a group of developers. But, if you were looking to help out with a new project, then this might be your cup of tea.
The cool thing about Github is how social the coding becomes. You can post an "issue" to a project, which can be tagged as various things like: feature request, bug, enhancement, translation, etc. Issues are discussed by using the comment section on each issue page. Some projects also have IRC channels or other additional ways of communicating.
So really it just comes down to what you are interested in. Once you narrow down your interests, you should be able to find some cool projects.
There is a website that also specifically exists to help people find open source projects
http://openhatch.org/