There's a free DNS service over at
http://www.no-ip.org, where you can download a free program, and it will update the DNS' IP direction to your new IP (Example: Your no-ip.org address is cd.no-ip.org w/ an IP of 55.55.5.5. Your IP changes to 55.55.5.4, the program will then change cd.no-ip.org's IP to 55.55.5.4).
The above is really good if you want to run your site off of your own computer (it'd probably be cheaper).
[I have to give thanks to Brandon though for telling me about this over the summer, so...thanks
]