You don't neccessarily need a domain name at all, if you go with a free host while you're just starting out (like pretty much everyone does) then you'll probably get given a subdomain.
Most hosts give you a free domain or offer a cheaper domain when you sign up with them as a sort of incentive. When I signed up with my host I took them up on their offer for one. Some people do not recommend this though, it could cause problems if you want to change host but keep the same domain name.
To be honest, a domain name is just a domain name, there's nothing special about it, but even so, I'd rather buy a domain from a reputable domain provider rather than "Dan's discount domains".
There are web-sites with just long lists of domains on them that they have gone out and registered, then they put them up for sale on their site. I wouldn't dream of buying a domain name from one of those places, it just seems very dodgy to me.