When it comes to exhuast, there's a ton of things you can do. It really comes down to what you want and how much you want to spend. The most common upgrades seem to be going to 2.25" piping (over the 2" stock) and some type of performance muffler. (Dynomax and Flowmaster are popular and are great for the prices) A couple guys have even gone ahead and put on dual exhuast. While this won't help performance any, and may actually hurt it a bit, if you want to do it go for it. There's not a lot of info I can give, you just have to find a shop willing to do it and see what they recommend as the best way to go about it. A high flow cat is also a good upgrade, see the "High Flow Cats" section for more info on them. Some people also replace the cat with just a straight pipe, or don't put any mufflers on. Like I said there's tons of different setups you can do.Check all local laws first to see just what you can and can't do. Below are a couple links to help get you on your way.

Mantapart.com - They list on their homepage that they now carry mandrel bent IM pipes and high flow converters for most applications.

A-1Performance.com - Besides carrying universal high flow cats and a variety of different universal mufflers, they also list some kits specifically for our cars. Below is some info I found looking around their page to help you get started. Note: If your not sure what to get, call these guys up, they were very helpful when I called.

SUPER TURBO KIT $141.95
1990 Beretta, Corsica w/ 3.1L
1990 Beretta, Corsica w/ 2.2L, Beretta GTZ w/ 2.3L
1991 Beretta, Corsica w/ 3.1L
1991 Beretta, Corsica w/ 2.2L, Beretta GTZ w/ 2.3L
1992 Beretta, Corsica w/ 3.1L
PN: 17476

SUPER TURBO KIT $136.95
1987-1989 Beretta, Corsica w/ 2.0L
PN: 17475


CyberAuto.com

DynoMax Super Turbo Exhaust:
90-92, 3.1, 2.2, GTZ - Part Number: 17476 - $150.3
87-89, 2.8, 2.0 - Part Number: 17475 - $150.36