If you can find it, Lottie's Bajun Cajun hot sauce is really good on taco bell stuff. Failing that, Buffalo Chipotle sauce is milder and smokier and also good. Failing that, use their "fire" sauce (better than their "hot" sauce) and then dose it with garlic. Or do what Allon and I do at work -- buy some powdered chipotle from Pennzey's and put it in a salt shaker and put it on everything. Even pizza.
Good hot sauce for taco hell