Dictionary Domains - Unregistered dictionary word domains for your side project
Domainz.io - Premium domains, for not so premium prices
Lean Domain Search - Find a Great Domain Name w/ twitter handle availability
estibot - Domain name valuation
Phey - Keep an eye on your (Upcoming) Product's subscribers/votes 📈
Park.io - The best place to backorder/drop purchase expiring ccTLD domain names.