+1 for a Mark D. If you have 93 octane available to you, I hear the chip he has for that is especially good. Regardless, watching the tach go off the end of the scale is pretty exciting.

I've heard that a lot of these Ebay chips just copy the exact same setup from Mark D, Conforti, Dinan, etc. It's more expensive but I think it's "better" to support the people who actually created these setups, rather than the guys who are just copying them.