clean and pretty
I guess Back to Black would be easiest to find, since my favorite, Turtle Wax "Black Chrome" is now only sold in the UK. Haven't tried this, but looks interesting, it is a black dye product: http://www.griotsgarage.com/product/car+maintenance/restoration/vinyl+convertible+top+dressing.do
Griot's vinyl dressing seems to work well - just don't overdo it or it looks too glossy. Ultimately I think all these products just put a temporary sheen on it.
Thats what I use. Use it on the rear spoiler as well, seems to hold up well, as I am only redoing it about one or twice a year.