Is there any DLC that you've purchased that drove you to buy the CD of a certain artist?
Recently for me, I just bought the Ghost Brigade - Until Fear No Longer Defines Us CD. Awesome CD, I'm very impressed with this band. Grain is a particularly good song. I first heard them on RB.
Originally, RB turned me on to Lacuna Coil. A band I absolutely love now. I've heard a few other songs that I've really liked, but wasn't in to much of the other songs they made.