Quite a few things out there. I used a product from Mequiars called Plastx. Picked it up at a local show.
The lense on my Trans Am was not as bad as what you are describing, but after several patient cleanings, it came out nicely. If yours is really bad, you may need something more aggressive, at least at first. Maybe one of those headlamp polishing kits.
T/A lense here...
TGO