willow bark? Your friendly GNC clerk should have been able to direct you to an asprin free alternative...
Anyway, a few of the thermogenics that do not contain asperin or chitosan are:
Yellow jackets, Zenotrope, Spirosome (tastes awful), BetaLean HP.
Xenadrine and most others contain White willow bark, so it might be best to avoid them.
Keep your body lean, your blood clean and your mind sharp. -Rollins