since you have the 3.8 engine there is quite a bit you can do to that engine, im not sure exactly to what extent, but i do know that it has a sizeable aftermarket do to that engine being featured in the Grand Prix, Impala, and Monte Carlo as well as several other GM models.
Transmission wise i know there are a couple different shift kits available.
Basically anything suspension-wise made for the Grand Prix or any other W-body will work fine. There is a handling kit from GM Performance Parts that im considering ordering right now.
There are a couple different brake upgrades as well, you can either upgrade the stock rotors and pads....or upgrade to 12 inch rotors up front(stock is 11 inches unless you have the Autobahn package)...you can also get F-body calipers to work with 12 inch rotors, but im not sure if they will fit with stock Intrigue wheels...the Grand Prix owners say they will fit with stock GP wheels, but im not sure about ours.
some basic mods would be the intake of course, with a high flow cat and u-bend removal.
a better place for you to check out for modding would be
http://www.clubgp.com because they have a lot more members with a bigger knowledge base, and your car is essentially a Grand Prix with a different shell on it...as is mine, but i have the 3.5 engine, so its a little different.
anyway, any questions lemme know, and definetely check out clubgp