We use the Data Quest system.

We are pretty happy with it and the times i've called for help they have been amazing at going out of there way to help me. You can call anytime of day or week and they will try to help you out as much as they can.

The software is fairly easy but can be tricky if your not good with computers.

I'm looking at them right now. I'm leaning towards the AEM AQ-1. Built in accelerometer, 3 digital inputs, and 8 analog inputs (4 of which will also do frequency so RPM, WG contoller, driveshaft, etc...)

They are less then $500. You can use GM sensors for just about everything.

The Innovative DL-32 is about the same price. I had someone suggest the RPM one, but honestly it seems pretty pricy for what you get?

http://www.aemelectronics.com/data-loggers-66/aq-1-data-logger-67/