Being in the business of starting new websites, I sometimes get the question, "What should I name my site?". If you already have a business (ie. brick and mortar) this is probably means less to you, because you of course want the register a domain name which matches your company name. However it is a question you'll ask when your company name is not available. The two articles below are regarding the two types of startup websites.
Once you've decided on your domain, register it for free here.
Just remember -- A great name can be a head start, but it won't get you to the finish line. A name is very important, but not if it keeps you from ever opening the business or getting online in the first place. In the end the most important thing is your business model and the execution of that business model.