Here is the list of service providers offering DNS service free of charge:
ScrubIt:
67.138.54.100
207.225.209.66
OpenDNS:
208.67.222.222
208.67.220.220
208.67.220.222
208.67.222.220
And VIP DNS
by gtei.net:
4.2.2.1
4.2.2.2
4.2.2.3
4.2.2.4
4.2.2.5
4.2.2.6
These DNS server proved to be reliable and fast. Recommended!

Some additional OpenDNS nameserver addresses
http://www.opendns.com/support/article/197
Thanks for the link, John Roberts. I’ve added two additional servers to the post and corrected a typo thanks to your link