iMusic Type in the name of the band that you're curious about, and listen. Sounds like crap, but it's enough to give ya an idea.
Personally, it doesn't me quite enough of an idea... It just lets me know if the band is worth checking out. Then I download off of Kazzaa and give them a real listen. If I'm gonna listen to it more than a couple of times, I buy the CD. If not, nobody loses.
This system causes me to dish out more on CDs than I usually did. Probably 4-6 a month.