From Domain Pigeon’s profile on Obsessable.com:
Domain Pigeon is a website that categorizes and makes available unclaimed domain names and Twitter usernames. You can search for specific names or browse through untaken domain and Twitter names by popularity or alphabetic lists. For a fee, you can peruse the shorter and more popular Twitter names of only three or four letters, or look for both Twitter names and domain names at the same time to see if they match. The site also lets you know how many of the sought-after names are left and when the next update will occur.