I hate armor all, it leaves such an oily residue and is not fun on stuff you touch regularly. Windex and a towel is the best thing to use. When I am going to a show, I mist down the whole interior with meguires it's amazing.
Now if you go into the heavy dirt I use a product called suds (amazing all purpose cleaner and it's non toxic and actually is edible) http://www.sudscleaner.com/
That product and a toothbrush (or larger bristled brush but not to exceed the stiffness of a toothbrush) just work the product in and wipe it off. leaves the plastic or ANYTHING clean and shiny. A bit expensive but I have had the same bottle for a year now and it's not even half gone. We have a whole case at work we still haven't gone through in three years. Honestly a case is a lifetime supply.