Given that you can register domain names for as cheap as 6.95$ per year ( see godaddy.com for details ), it might make sense to register your Primary keyword phrase for use as the domain name to your website. If the .com version of a domain name is taken then try .net version or the .cc version. It doesn't matter to Google.
When registering a domain name seperate each keyword in the domain name with a hyphen, otherwise google will not be able to recognize the phrase and will think it is a single( usually nonexistent ) word. Here is the correct format to use for domain names.