What do you want to accomplish?
A few basic mods to get you started:
Gears - No HP added, but you will have more low end power. 4.10s are popular but I prefer 3.73 for a better balance. Gears will throw your speedo off.
Tune - You can pick up a Diablo or SCT handheld tuner for a few hundred dollars. I prefer the SCT. This will allow you to advance your timing as well as compensate your speedo for your new gear ratio. "If you mod to the point of needing a dyno tune your tuner will use this device to load your tune." Consider what your local guy is using when you make this purchase to avoid having to sell it and buy a different kind later on.
Shifter - The stock shifter sucks. Drive a friends car to feel the difference. There are several brands available.
Intake - Exhaust : These give you more sound than power but it all adds up. A better breathing engine will perform better all around. H-pipe for deeper muscle car sound. X-pipe for raspy.
These are a good start and other than the intake possibly being replaced if you go forced induction you won't be buying parts now just to purchase different parts later.
Enjoy your car