Have been using turtle wax liquid ice, which is really easy to apply and lasts for a good few washes....... however I have just watched the you tube video on this g-techniq C4 permanent trim restorer and if it is to be believed tha it lasts two years good be a better option as it would not need to be re-applied so often. Does it last as long as it says tetchmeister.
I've also heard that the G-Techniq product is about as good as it gets. However it is quite expensive for the amount you get (even though it does go a long way and last a long time.) Other less costly options but that also get good marks on Detailing websites are:
303 Aerospace Protectant
Ultima Tyre and Trim Guard
Wolfgang Exterior Trim Sealant
Simoniz New Look