Linux kernel development
LinuxMM Linux memory management wiki
Linux distributions open for participation
Linux Security detailed Linux security news site
Linux Weekly News - follow the kernel link (changes weekly) (the current kernel page is always http://lwn.net/current/kernel.php3).
Kerneltrap - news on various free OS kernels (Old, have contacted Jeremy)
Kernel Traffic (link to Internet Archive) - a digest of what was discussed on the Linux-kernel mailing list (original site has disappeared)