Loads of products on the market, but its only when you look at what they do that they start to make sense.
The black plastic trim on your car is made originally from oil (all plastic is)... as the sun dries the plastic out, it fades, goes brittle, and looks horrible.
What you need to do, it put some natural oil back into the plastic - sounds odd but true.
The best thing is to use some oil (cooking will do, but peanut is best as its thinner) and work it into the plastic. You'll get a lovely black shine back. Some people even put peanut butter on their trim to get the same effect - i'd end up eating it all though
If you want to use a product, AutoGlym bumper and trim care is among the best I've used. Its a green goo that contains all the oils to restore shine, and a silicon to seal it in.