El Diablo Viper,
If you are serious about road racing the car, the best wing and splitter is the last iteration of the ORECA/factory GTSR wing and splitter. McCann Racing makes them and they are sold through Archer Racing (218-727-4806). The front runners in the Viper Days Viper Racing League run this setup. It is all carbon fiber and very limited production so bring your check book. There are also other good wings out there but be careful to select a wing and splitter with high lift to drag ratios. All wings are not created equal and some of them out there only generate downforce because of the sheer weight of them.
This splitter sits very low so I anticipate you would have to remove it for street cruising or risk damaging it. With the wing and without the splitter there will be too much rear downforce at speed so I wouldn't go "racing" on the street or track in this configuration. Remember, if you do a rear wing, you also need to put on a front splitter to balance the car. Keep this in mind when selecting to get a set that will work properly together.
In response to GTS Bruce's comment, you will lose a few mph top speed, but you will not go slower on a road course because cornering speed, corner exit speed, and braking will be dramatically improved (which is why your lap times will drop). Why do you think all race cars use aerodynamic devices to generate downforce/reduce lift.
Here is a link showing this wing and splitter setup both painted and natural carbon fiber.
http://vca1.viperclub.org/ubb/Forum14/HTML/011126.html
Check out a Viper Days event, lots of different wings show up there and you can see what they look like and ask a lot of questions.
Good luck with your decision, you can't go wrong because the car looks great both with and without a wing/splitter combo.
Best regards,