Found this thread and thought it was cool, so I'll bring it back to life.
Here is what I think is under rated
Mothers Carnauba cleaner wax (and most other mothers products, but this one especially) - This is a great one step that leave quite a bit of depth and good protection, great for people who dont wanna pay for polishing, sealant or anything and just want it waxed (talking about pro detailing). Also cheap and easy to find and not to mention use.
BlueMagic Leather Cream Condtioner - This is cheap and works great to restore leather. Leaves a satin finish and I love it because it makes the seats stickier (not really sticky, just grabs you better, like it was when it was new) which is great for going around turns
Blue Coral Upholstery Cleaner Dri-Clean - This is the best upholstery/carpet and any other like material cleaner I have used. And its cheap and available at the local walmart.
Thats all I can think of for now.
So now lets hear what people think is underated a year later.