http://www.godaddy.com
$8.95 per year. Have not had a problem yet.
What you want to do is run your own Domain Name Server (DNS)
You can do this with Mac OS X client. You can go to macupdate.com and look for dns and find an app that will help set up the config files. It is fairly complicated. Ideally you would read "DNS and BIND" from
http://www.ora.com
That would give the the knowledge you need to realize that any registrar should let you run your own DNS server, and once you do that, you do not need to have www in your domain.
What you buy is the last two parts of the domain name, like
macrumors.com
then you create a zone file that lists all the hosts in that domain
www
mail
smtp
dns
ntp
Then you create a reverse zone that lists
all the ip addresses first and then tells a person what the name of the computer is
128.2.6.48 titan.net.cmu.edu
Then there are MX entries, SOA entries, take a couple of days to read the book above if you really want to control your own dns.
If you don't, why don't you go to
http://www.dyndns.org
they will host your dns, allow you to resolve a hostname on a computer whose IP address is not static. They have a nice interface for adding names.