I just added a pair of Super Swamper Boggers to the rear; you can view those details HERE.
At 77k miles, I bought some tires and wheels to replace the stock ones - Interco Super Swamper TSL/SX's, 38.5x14.5x16.5, and Extreme Hummer aluminum alloy wheels, with braided stainless CTI lines. I ordered them through Extreme Hummer [now called "Extreme4wd"] in Georgia. I have now gone through two sets of these tires, at about 30k miles per set. They are great off-road, and better than I expected on road.