One Word Domains - Database of all available one-word domains
Transferslot - Easily buy and sell side-projects
Undeveloped - Domains you never thought were available
Flippa - Flippa is a platform for trading websites.
Domainz.io - Premium domains, for not so premium prices
BuySellEmpire - To help owners/vendors buy and sell high-quality domains/websites for a better price.