By SEOmoz has has a great list of rules to follow when coming up with domain names, check it out:
- Brainstorm 5 Top Keywords
- Make the Domain Unique
- Only Choose Dot-Com Available Domains
- Make it Easy to Type
- Make it Easy to Remember
- Keep the Name as Short as Possible
- Create and Fulfill Expectations
- Avoid Copyright Infringement
- Set Yourself Apart with a Brand
- Reject Hyphens and Numbers
- Don’t Follow the Latest Trends
- Use an Ajax Domain Selection Tool
Most of those rules are straight forward, but you can read a complete description of them here.