What are the rules for choosing a domain name?

1. characters allowed abcdefghijklmnopqrstuvwxyz0123456789-
2. cannot start or end with a hyphen (-)
3. UK Rules: length between 2-63 characters
4. UK Rules: 2 characters allowed if 1 letter and 1 number
5. US Rules: length between 2-67 characters including .com
6. info Rules: length between 3-68 characters including .info
7. biz Rules: length between 3-68 characters including .biz