Dot TK, that is what I use. You just have to get a minimum of 25 hits every 90 days to keep it. As long as you can do that, it is free for a .tk domain. Yep, totally free. For a real domain. As in yourdomain.tk. Pretty cool. Check it out:
http://dot.tk/.
Its what I use and it works great!
If you were looking at getting a .com, .org, or .net. Goodluck. Those will cost you.
The closest you can get to free on those, is if you do some sort of service, or sign up for something, and in the end, you will usually wind up paying anyways.