You'll most likely hear alot of people recommend savvy products, but i think you need to have a 2003+ TJ with auto transmission. This is nice because it's very light weight and nearly flat against the frame rails. Savvy makes a good product, i own a bunch of their other armor.
Under Armor 2003+ Auto Transmission
Personally I went with the Rokmen tummy tuck, It's made of steel but not extraordinarily heavy. I've given it a beating and it's in good shape. Of course you'll get large scratches and gouges going over the rocks with any skid, and if you want to avoid rust you should get down there with some spray paint and cover the bare metal ( as you should with any steel skid )
Rokmen Gear Up....Rok On