If you don't want to go "full" exhaust (headers, etc), I recommend Snake-Oyl cat-back exhaust. I think they're 2 1/4" pipes. They make the Viper sound like a classic V8. Lee had his put on at Woodhouse when bought new (I think at Bill P's recommendation). Has a nice idle, burbles at the release of the gas, and throaty at WOT.
ViperJoe is right, you should go to a VCA meet and listen to the exhaust notes. I'm sure owners wouldn't mind starting them up and drive-by or take you for a short ride. I think the best way to hear the exhaust is at a dyno day. You're right there when the car is idling, starting up at part throttle, you hear it on the release of the gas, and at WOT.