Who Should Register A Domain Name
You should. Period.
If you're going to have a website, it's absolutely vital you register your own domain name. Everyone who wants their website to look professional, (and it must, if you want to make money off of it...), should absolutely have one.
Many people who use free "web design" or web hosting services think it's okay to have domains like "www.geocities.com/myname/mycompany/longname.html". You will lose valuable visitors with something like that. Even a shorter one like geocities.com/mycompany is something that will turn potential customers away.
It's extremely affordable to register domains, so there is absolutely no reason to skip this step.
Register A Domain Right Now
Unless you need more details about why you should have one or how to choose one, we recommend you jump directly to the "where" page and register a domain immediately. Good domains are becoming increasingly difficult to obtain, and the one you want may be gone tomorrow, if it's not gone already.