Recently Google announced the availability of their DNS servers for public use. There are a few reasons that changing the DNS servers from the ones provided by your ISP could be beneficial. Namely speed, security, and control. Google are promoting their service through the idea that it will be faster than your ISP, other services such as the one provided by Comodo focus a little more on the idea that using theirs will be more secure. Of course this is all relative depending on how good your ISPs are, so below I have listed a few to try:
Google Public DNS:
Comodo Secure DNS:
There is also a service called OpenDNS which requires registration. This however does give it an advantage, as you are then able to log in to your account and make changes to its configuration as well as view logs.