• .aero - air transportion; restricted
• .arpa - reserved by the Internet Architecture Board; restricted
• .asia - Asia-Pacific region; restricted
• .biz - business and commerical use
• .cat - Catalan language and culture; restricted
• .com - commerical, personal, or any use;
• .coop - cooperatives; restricted to Co-Op organizations
• .edu - post-secondary educational institutions; United States only; restricted
• .gov - United States government orgs at the federal, state, and local levels; restricted
• .info - informational use
• .int - international organizations established by treaty; restricted
• .jobs - employment-related; restricted
• .mil - US military; restricted
• .mobi - mobile device based; restricted
• .museum - museums; restricted
• .name - individuals;
• .net - originally for network infrastructures; today unrestricted
• .org - originally for organizations; today unrestricted
• .pro - professions; restricted
• .tel - services between telecom and the Internet; restricted
• .travel - travel agencies, airlines, hotels, tourism bureaus; restricted

The only six open tlds to register a name in are com/net/org/biz/info/name.

As of July 2009:

• All 3 letter possibilities are gone on .com
• All4 letter words are depleted on .com
• The most popular registered domain name length is 11 characters
• There are 255,000+ domain names that are 32 characters or longer
• All of the top 10,000 family names are registered as a domain name
• The most common letter to start a domain with is S
• More than 270,000 domains contain the sequence SEX