If your domain is available.. be sure to buy your domain, immediately!
If your domain is taken then first try a variation on the name. BusinessName-NewYork.com. or BusinessName-Description.com
If your name is often misspelled you may want to purchase a misspelled version and setup that domain to redirect to your website. This way if a misspelled name is typed it can still be directed to your website.
NOTE: ALWAYS purchase a Domain by yourself. NEVER let someone else buy or register a domain for you. If another registers for you they will use their own name and credit card info. This makes it very difficult for you to verify that you are the owner of the domain.
AGAIN, NEVER let anyone buy a domain for you!!