Drivetrain
An aluminum driveshaft will weigh less (13lbs instead of 20lbs+, run about $425) and therefore contain less rotating mass. This will waste less power and allow more to get to the rear wheels. The performance improvement is noticeable and I definitely recommend one. Brand new they can be expensive, so go scope out the junkyards for a 1LE camaro aluminum driveshaft. MAKE SURE IT WAS NOT DAMAGED IN THE WRECK! If it is even slightly bent, vibration will be a HUGE problem! Get one off a car that was in a minor wreck only. In addition to the rear wheel power increase, this better-balanced aftermarket driveshaft will also solve the vibration problem that seems to happen on fourth-gens at around 90mph (I've heard). Note: On third-gens, the driveshaft is interchangeable on the manual/auto tranny, not certain about fourth-gens. Now there are even carbon-fiber driveshafts (10lbs., $750) that are even lighter! Wow! These can handle up to 1200hp and have the highest critical speed of any driveshaft! Be sure to install a driveshaft loop with new driveshafts (and stock ones if you're smart) to prevent high speed catapults. They are no picnic.
This can make a huge difference in acceleration. But remember, higher gears result in better of-the-line performance, but sacrifice top speed. 3.73:1 seems to be the favorite all-around good gear. I wouldn't go higher unless I had a 6-speed with alot of top-speed to spare. (about $279, w/seals & gasket)
In a manual tranny, a shorter throw stick is a must, you'll be asking yourself, "why didn't I do this sooner?" When racing, the significantly shorter throw is, ...so choice. But in automatic, the stick isn't really worth it unless you are changing the valvebody. If you get one, take your time installing it because I have heard of leaking problems. I don't know if it was due to bad design or a sloppy install. Valvebody shift improvment kits will drastically firm up the shift, but after a while I have heard they can be extremely uncomfortable. It's no fun when you just want to cruise and the tranny is snapping your neck back on every shift. A stronger servo (corvette type) from TCI would be the best bet for mild shift improvement on an automatic.
For camaros equipped with automatic transmissions, a higher stall torque converter can improve performance. Stock converters (700R4 tranny) lock up at around 1300-1600rpm. Upgrades start at 2000rpm for stock or mildly modified engines. It will deliver a more powerful launch and better power after shifts. The stall speed (lockup rpm) greatly depends on the engine, specifically the cam. The stall speed should be near the torque peak of the engine. You should consult a professional when buying in order to get the right one for your car. Typically, if an engine makes less than 300ft-lbs of torque, it should stay at 2500 stall or less, where as a 400ft-lbs torquer can have a 3000+ stall converter, dependent on the rpm that the torque peaks, of course. Consult a pro.
You can buy the skip shift eliminator made by JET and a couple of other manufacturers, installation is quick and easy and the part is only $20-30. Or you can buy a resistor at radio shack and do the same thing for only pennies! Click the link above for directions. To disable the shift light, disconnect the white wire (pin 15) on the blue connector in the PCM.
Shifts are much firmer. More solid mounting (polyurethane instead of rubber) gives a better all-around feel. Less vibration dampening so expect a bit more vibration and noise, but well worth it! Only costs about $30, and installs in 15-20min.