Here is what I do.

Every once in a while, I look at the top 100 metal bands on MySpace. To do this, you;
1) Go to MySpace Music
2) Got to top artists
3) Select the Metal genre
4) the bands are ranked by the number of plays.
Then, if I hear a band I like I will go and buy their songs on iTunes.

As for the radio, try listening to Harddrive. It is a national syndicated rock program, and through I learned about Evans Blue and HELLYEAH.

As for paying extra money for a real CD, I only do that if I really like an album. Usually albums have a few songs I don’t like, so I just buy the single tracks on iTunes.