I use FreeDNS for my Raspberry Pi too, and I really like it. One can provide his domain for DDNS on afraid.org, and then you basically can create a subdomain for DDNS, so there are A LOT of domains to choose from. And they provide way more options for assigning your device to a domain than a lot of others do...
Only thing: I use ddclient as my DDNS client, and the version that is in most of the distros repos doesn't support FreeDNS, so I had to compile it myself. That shouldn't be a problem though, and I think there are other clients that support FreeDNS too..