http://freedns.afraid.org/ has an absolutely huge selection of donated domains you can get a free subdomain of. The problem is, you're not guaranteed that the subdomain you register is going to be yours for any guaranteed period of time, since the owner of the domain could take it back whenever they want. If you stick to domains owned by "josh" (owner of the site) or "ukto" who provides the nice us.to and uk.to domains, you should be okay. The oldest domains on the website have been online for over a decade.
If you want to host from a dynamic IP (changing IP once a week or more), no-ip is perfect (though there's other dynamic DNS solutions that aren't as commercial) since it has an automatic update client that will get your domain's IP updated in around 10 minutes. You can use no-ip and freedns to achieve something like linking foobar.us.to -> foobar.no-ip.org -> (your dynamic IP).
