Anyone that has ever used Google's Adwords External Keyword Tool, knows just how easy it is. If you haven't used it, you should. I'll forewarn you though, you'll get hooked!
Simply type in a word or a group of words, and you've got a list of keyword suggestions sorted by volume. Now, you've got domain name availability (.com/.net/.org) seamlessly integrated as well!
There's a reason why there are so many domainers in the world and only so many you've actually heard of. It can be VERY lucrative, but you definitely need the right domains. Finding a keyword domain with high search volume is like finding money! If you were to make $5/day off of a single keyword domain, what would 10 domains get you? 100? 1000 domains?
Some people buy good domains to resell them for a profit. Others buy domains to make money off of type in and search traffic. Some even build beautiful sites on their domains and can often times pull off first page rankings based on their keyword domain alone. Whatever you do, the secret to success is simple: Lather, Rinse, Repeat!