From the Kernel Janitors website ([http://www.kerneljanitors.org]): «We go through the linux kernel sources, doing code reviews, fixing up unmaintained code and doing other cleanups and API conversion. It is a good start to kernel hacking.»
"The Kernel Janitors Project" is a good point to start for newbie kernel hackers. The project maintains a TODO list ([http://kernelnewbies.org/KernelJanitors/Todo]) from which contributors can pick a job which fits their skills. The tasks are mainly code cleanups so one can dive into kernel code without knowing all the technical details already. It's also a good point to learn about how to (or how not to) submit patches to the kernel.
The project keeps its own mailing list ([http://vger.kernel.org/vger-lists.html#kernel-janitors]) and the maintainer (Alexey Dobriyan at the moment) also irregularly produces a patchset which can be found on [http://coderock.org/kj/].