Having a tuned motor under the hood is cool. Having a server rack full of electrical gizmos in the cabin to control the tuned motor is cooler than Fonzie on ice. Gadgets are a way to purposefully floss what you got. It's the difference between James Bond using a cellie to control his 7-Series or a plastic-framed Etch-A-Sketch. Both work, but only one can pull the firme heinas quicker than Speedy Gonzales on an iPod loaded with Rock en Espaol. Arriba, arriba! Andale, andale!
Andale-ing on, the following is a semi-categorized list of cool shite that either reads your car's parameters, controls stuff, upgrades your ECU or sparks up the ignition. In other words, more fun with electrical pulses than a battery-operated harikata (isn't that technically a vibrator? - RC).