Go to the website of the Secretary of State for your state. There will be a registry of corporation names, where one can check to see if that name has been registered. It is very easy.
Originally Posted by: Nonstopdrivel
Well, usually. Some state's secretary of state websites are a pain to navigate. Iowa's, for example, is a royal pain in the ass to navigate. And Nevada's still prefers you use Internet Explorer! On the other hand, Wisconsin's was, last time I looked, quite good.
It also depends on where your business is going to be done. As far as I know, there is no national registry of names (since unless you're a bank or such, corporation/partnership/sole proprietorship law is all state law). So you'd want to run a check on any state where you'd expect to be doing business.
The exception would be if the name is trademarked. Then you'd need to go to the US Trademark Office. I don't know how that works, but my guess is there's a website.
But even if the name isn't trademarked, you want to do as Rourke said, and check out the Secretary of State site. If you do start a business, you're going to want to make a "d/b/a" filing with the Sec of State. Stands for "doing business as..."; each state calls it something more official sounding, of course. But generally its a very easy, simple form with a pretty small fee.
(I'm assuming you're talking about starting a business as a sole proprietorship, not as a corporation or limited liability company. Those obviously are a bit more complicated, though also relatively simple and not particularly expensive. (As long as you don't eff it up like I did and overpay for my Nevada sub-S company.) Depending on what kind of business you're talking about, you might want to consider something incorporated -- it can bit bit of a pain in the ass with the extra paperwork, but it can often be a really good idea to have a "separate entity" that limits your liability, etc.
And do not be conformed to this world, but be transformed by the renewing of your mind, that you may prove what is that good and acceptable and perfect will of God.
Romans 12:2 (NKJV)