Ok, so you've setup a web server. Wonderful. Now you realize that for the world to see where your server is, you need some method of telling the world's computers where your site is. DNS, short for Domain Name System, sometimes referred to as a Domain Name Server, or Domain Name Service, translates the intenet name you type in (i.e.; dirtcheapdns.com) into a series of numbers. It is actually the numbers that point to the appropriate server on the internet. Then your computer knows what address to go to. Most web, mail, dns, etc servers are on a Static IP Address. Think it it like phone numbers. If your telephone number were to constantly change, how would people reach you the next time they tried to call you? A Static IP address simply means the server always has the same set of numbers. Most dial-up and DSL connections have Dynamic IP Addresses, meaning they obtain a different set of numbers each time they connect to the internet. While it IS possible to have a web server on a Dynamic IP Address, and many people do this, it is not always easy for a beginner to learn about it. You should check HERE for more information on setting up your server for Dynamic DNS

Getting a DNS Server:
Cheap DNS is good! Free DNS is beter! If you have some experience with servers, and have enough public IP addresses available, you can run your own DNS Server.

One of the most commonly used is ISC BIND, and it comes packaged with most Linux Distributions. Many of the commercial DNS providers also offer some sort of free service for small operations, or people on dynamic IP Addresses.

Another thing to check is you domain registry. For example, www.GoDaddy.com offers DNS Service free with their domain names.

Commercial DNS providers:
Normally, assuming you have a Static IP Address, you can save yourself a lot of time, trouble, and money in the long run by just having your DNS hosted somewhere else. Also, you normally get additional benefits, such as server monitoring with notifications of when your server goes down, dns failover, to point visitors to another server when your primary server goes down, etc.

Prices vary greatly, but one of the best I've found so far has got to be DNS Made Easy. They will host your DNS for 50 domain names for under $30.00 per year, as of this writing... I use them myself. So far, they have yet to go down. Another good one is EasyDNS.