We recommend you use Google's Public resolvers:

Google Public DNS IP addresses

The Google Public DNS IP addresses are as follows:

• 8.8.8.8
• 8.8.4.4

You can use either number as your primary or secondary DNS server. You can specify both numbers, but do not specify one number as both primary and secondary.

You can read more after the link: http://code.google.com/speed/public-dns/docs/using.html