Energy Suspension: Energy suspension offer's awesome polyurethane bushing's that increase handling and last a longgggggg time. Information can be found at http://www.energysuspension.com. Swaybar bushings part number is (9-5136) or (9-5168) for greaseable fittings.
Tires: Tires keep you in control of your car. Hard tires last long but handle terrible. Soft tires handle great but don't last long. I would recommend Goodyear GS-C tires. They provide a nice ride, great control in rain, reasonable tread life and very good cornering. Keep in mind if you drive your Grand Prix around the 140-150MPH (yes you can get the Grand Prix's to those speeds very easily) area that you have Z-Rated tires. 225\60\16 Goodyear GS-C tires will cost about $140.00 each. The best place to find tires online is at http://www.tirerack.com
Rear Anti-sway Bar: The stock anti-sway bar on the front is thick and provides good control. However the rear anti-sway bar is thin. The rear bar is only 1\2 inch thick and bounces around a little bit. ADDCO industries has the solution. They have a anti-sway bar for the rear that is 7\8's of an inch thick. That's almost double the thickness from the stock one. They also offer urethane end links for the bigger anti-sway bar to further increase handling. Part number for the rear anti-sway bar is 474. Part number for the urethane end links is 612 and both can be ordered from the manufacturer at http://www.addcoindustries.com