Domain Purchasing

Ok, soon I'll be purchasing a domain name to go with a host, and I'd just like a few questions cleared up.

What's the difference between one domain name company and another? One site offers $35 for one year, and another offers $15. Does where I buy mine from affect anything?

I was under the impression that it's up to the host whether or not you have pop-up adverts. Am I right in thinking the domain has nothing to do with this?

If the last question in the first paragraph is yes, anyone recommend a good one? I'm not too bothered about an email address, but my host says I'll get one anyway. Or something.

Thanks. :)

Try www.godaddy.com. It's a really good one, and one of the cheapest.

Ad banners should have nothing to do with purchasing a domain. If they try to make you use ad banners go somewhere else to buy it.