Domainz.io - Premium domains, for not so premium prices
Park.io - The best place to backorder/drop purchase expiring ccTLD domain names.
Domcop - Domcop allows you to find 2million+ expired domains and all of its pat information.
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.
Selldom - Make money from your unused domains 💸
Catched - Catched is a web service that allows you to perform all tasks related to selecting the domain name of your website from domain name research, domain name building, and buying.