Domainsbymail.com
Sells lists of unclaimed domain names in multiple price categories.

WebExplode.com
Expired domains, dictionary domain lists, trademark protection reports, and other resources for domain owners.

Domains Bot
Search and track expired domain names.

3LA - 3 Letter Acronyms
Free lists of available three letter-numeral .net and .org acronym domain names.

Red Hot Domain Names
Free expired domain name lists.

DomainEye.com
Selection of services for identifying available domain names.