One Word Domains - Database of all available one-word domains
DAN.COM - DAN is on a mission to make unused domains accessible to all
Lean Domain Search - Find a Great Domain Name w/ twitter handle availability
dofo.com - Domain search platform Dofo.com gathers all registered (350 million) domains of the world in a single place. Dofo also brings together all the domain names that are on sale, provides useful features, all completely free.
Tool.Domains - Search free to register expired domains
BrandBucket - The original marketplace for business names and creative domain names.