Amazon Route 53 - Amazon Route 53 is a highly available and scalable DNS web service.
One Word Domains - Database of all available one-word domains
GoDaddy DNS - GoDaddy DNS helps manage website performance, reliability and security.
Domainz.io - Premium domains, for not so premium prices
NSONE - NSONE is a high performance DNS service providing unparalleled control over where end users are routed.
Undeveloped - Domains you never thought were available