The Nouveau project is still maintaining the Nouveau project TODO list for those looking to help out with this community-based project for reverse-engineering NVIDIA GPUs in order to provide a full-functioning open-source driver.
The TODO list is a bit outdated, but was revised last month with some completed items. Tasks on the TODO list range from working on the kernel DRM driver to working to improve Nouveau driver power management, a few xf86-video-nouveau DDX driver changes, Mesa tasks, and other general items.
If you're not wishing to dive into code, you could help them out as well by simply testing the latest Linux kernel and Mesa/Gallium3D Git code for Nouveau on your NVIDIA GPU(s). They could also use a lot of help in trying out the largely rewritten Nouveau DRM driver that's to be merged for the Linux 3.7 kernel but could use extensive testing to avoid regressions hitting the Nouveau kernel component.
For other information head on over to the Nouveau Wiki or drop by #nouveau on FreeNode IRC.