From the Kernel Janitors website : «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.»

If the site is down, there's a local copy of all the content at: http://kernelnewbies.org/MigratingInProgress

"The Kernel Janitors Project" is a good point to start for newbie kernel hackers. The project maintains a TODO list 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/.

UPDATES:

There's a newer Kernel Janitors page at http://code.google.com/p/kernel-janitors/, but it seems that some of the content from above hasn't been moved over, so you should look at both sites.

There's an article, Fixing the Kernel Janitors Project, with criticisms and suggestions about the project. Some suggestions to kernel newbies:

• don't focus so much on fixing whitespace problems
• avoid fixing compiler warnings because the goal is to fix the CAUSE of the warnings (which is usually not obvious), not just to make the warnings go away
• test the kernel on a wide variety of hardware and submit good bug reports
• acquire an obscure (i.e., not yet supported) piece of hardware and write a driver for it (might require some mentoring though)

UPDATES 26 Nov 15:

The Kernel Janitors Mailing list seems pretty active. Still looking for a website.