I just wrote a new entry on the Gentoo Wiki: Howto Dynamic DNS with EveryDNS
I’ve been using these guys for a number of years, and have never had any problems. The great thing, unlike the other free services, is you can point your own domain wherever, instead of getting subdomain.something.com only. Plus, how they give you total access to the DNS record settings is really nice. Highly recommended.
That, and I just love writing HOWTOs.