Follow Linux kernel development with git

1. Install git. Some dists have it in repos, there are packages at http://git-scm.com/download
2. Run git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git

Now you have the latest snapshot + revision history back to 2.6.12-rc2 which you can update with git pull (My linux-2.6 folder is 778MB)

Check for updates on http://kernel.org/ or just finger @git.kernel.org
I put this line in my crontab:
01 16 * * * cd /files/Public/linux-2.6; /usr/bin/git pull

Ref:
http://kernel.org/
http://www.kernel.org/doc/local/git-quick.html