http://www.hn.org - its Hammer Node.
For free, you can get whatever.hn.org.
You can either manually update the DNS entries on their web site whenever your IP changes, or you can try one of the linux perl-based scripts.
For $75, you can buy your own domain at places like nic.com. And then just use hn.org for the dns host, and you can serve
www.whatever.whatever off your computer.
Oh, and incase you didn't know, you can enable web sharing in the system preferences, under 'Sharing'.
Let me know if you have any questions!