Hopefully you know what DNS is (otherwise lookee here).
If you are a small business or home user, chances are your current DNS is given to your firewall/router automatically by your service ISP.
That allows the ISP to track every website ever visited from your location, and remember, the ISP knows exactly who you are - they are the ones that can and do match up your IP address with your name, address, account, and billing info.
Plus they tend to be slow. How slow? Check Steve Gibson's (the famed GRC.com) DNS Nameserver Performance utility.
An excellent and widely accepted alternative is to access your firewall/router's configuration pages, and in the WAN, Network, DHCP, or similar area, enter the IP addresses for the free OPENDNS.COM DNS servers.
Another good thing about OPENDNS: very often other Domain servers, when you mis-enter a domain, will direct you to a commercial search page of their own. OpenDNS does not direct you to a commercial page.
OpenDNS also warns when entering dangerous sites.
Finally, if you set up an account (you don't have to), even a free one, you can further admin your domain-name service - you can read up on it if you want on their site, OpenDNS.com.
Two of the primary IP addresses for their DNS servers are:
208.67.220.220
208.67.222.222
