I havent heard much about getting free domains!!! May be only some site which provide some free URL redirections or some domains without any DNS.
But may it be free domain or an url redirection they all hav Ads displayed on your site and most of the times your site appears in a frame.
The best option here would be buy a domain and put your own ads. May be doing this at the end of the year by the time your domain is about to expire you atleast could get some funds through those ads whith which you can renew the domain
Or may be if you are good enough you can always make a lifetime earning from it. Rather then earning for someone else