I buy white tees in those multi-packs all the time and I'm always looking for new ways to spice them up.
A plain white tee is like a blank painting canvas to me. Except my painting supplies are mixed media and my brushes are my hands.
1. Take a tee and cut it down into a loose tank like the one above, or just leave it as is. use your imagination and stay unique :)
2. if you don't have any extra scrap pieces of leather/pleather around from a cut up jacket or something, an alternative is black vinyl. you can buy it in huge rolls at wal-mart for fairly cheap.
3. cut out your design with an exacto-knife or scissors (sharp ones).
4. pin your cut out to your shirt and sew it on :)