Free & Public DNS Servers (Updated July 2014)

Most of the time, your ISP automatically assigns a primary and secondary DNS server when your router or computer requests network information via DHCP. But what if those ISP-provided DNS servers aren't reliable or you're troubleshooting an issue and you suspect that DNS might not be working properly? 
Luckily there are several free DNS servers that you can use instead of the ones assigned to you.

Provider	Primary DNS Server	Secondary DNS Server
Level31	209.244.0.3	209.244.0.4
Google2	8.8.8.8	8.8.4.4
Comodo Secure DNS	8.26.56.26	8.20.247.20
OpenDNS Home3	208.67.222.222	208.67.220.220
DNS Advantage	156.154.70.1	156.154.71.1
Norton ConnectSafe4	199.85.126.10	199.85.127.10
GreenTeamDNS5	81.218.119.11	209.88.198.133
SafeDNS6	195.46.39.39	195.46.39.40
OpenNIC7	216.87.84.211	23.90.4.6
Public-Root8	199.5.157.131	208.71.35.137
SmartViper	208.76.50.50	208.76.51.51
Dyn	216.146.35.35	216.146.36.36
censurfridns.dk9	89.233.43.71	89.104.194.142
Hurricane Electric10	74.82.42.42
puntCAT11	109.69.8.51

Note: Primary DNS servers are sometimes called preferred DNS servers and secondary DNS servers are sometimes called alternate DNS servers. Primary and secondary DNS servers can be "mixed and matched" to provide another layer of redundancy.