I think if you threw Mozart on a T-Shirt, so long as it looked 'different' kids would buy it. It would be weird and different and they'd wear it.

As far as shirts I've owned, I've purchased almost every Smashing Pumpkins shirt I could get my hands on. They've been my favorite band since I discovered them. I love Billy Corgan as a writer and try to get everything he does out of my appreciation for his music. This leads me to say that one of the ugliest band shirts I've purchased was a Zwan shirt. I own two Zwan shirts, one I ordered before their CD was available, and the other I picked up at a concert. The sad part is the one I got at a concert is a really light (sky?) blue with rainbow on the front. The rainbow has a crack in it but it's still a rainbow. It's my gay shirt.

I've had my Modest Mouse shirt for about 4 years or so, maybe longer. And I purchased a Death Cab for Cutie shirt about 3 years ago but they sent me the wrong one so I gave it to my friend since it was a baby doll T. Those shirts were different in the sense of, at the time, no one had heard of those bands. And the one or two times you run into someone who does know the band it's fun to talk about them and your favorite songs. This happened one time while out to eat, my brother had his MM shirt on and the waitress loves them. We talked to her for a few minutes about it and it was fun to talk about the music we really love.

Other band shirts I own:

Kiss - one of the best shows I went to, bought at concert
Pepper - given to me at their show