Search engine optimization is powerful, but relying entirely on search for visitors is a bad strategy. Many of the most successful small brands get most of their visitors DIRECTLY while still ranking extremely well on search engines. Examples are seochat.com, searchenginewatch.com, seomoz.org, copyblogger.com, grokdotcom.com, searchengineland.com and many more. Ironically, those sites do so well that, if you were to eliminate their search engine rankings they would maintain their mind share and do just fine.
Branding is a topic of its own, too large to cover here; you can learn more by doing your own research. To add to this section, content is one of the best ways to brand a site online, but content has to be in the form of a unique idea or a new approach to things. I cover this concept in detail in my articles on online copy writing.
Learn About Domains from the Pros
Frank Schilling is the biggest domain broker in the world. Though he doesn't do SEO, he knows the domain business from the inside out from all perspectives: selling, buying, pricing, parking, SEO, search and more. You can watch his 40 minute speech where he shares his story (from which you can learn as well) and talks about domains in general. Also check out his Seven Mile blog, as there's a lot of wisdom in his posts
Conclusion
Some basic domain guidelines from an SEO perspective:
Go for old domains over new ones.
Go for domains that have at least one of your keywords in them (because of anchor text benefit).
Don't use dashes.
.INFO and .BIZ have low trust levels.
Go for .COM over anything.
.CA, .AU and other local domains are as good as .COM if you're after local markets.
Short, easy to remember domains are best for branding.
Use hosting in your country if you're after local markets.
Search Optimization 
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