I had 31x10.50x15 BFG TA/KO All-Terrains on my Nissan Frontier and loved them. They were quiet and gave a smooth ride, but were still rugged. The price tag made my wallet sad.
Once the X-mas holiday is over with I plan on getting a set of the General Grabbers (AT2) from TireRack to try out on the Explorer. I haven't decided whether I'm going to stick with the stock 235/75/15 ($77) or go with the 31x10.50x15 ($90) instead.
I've heard nothing but good things about the General Grabbers, even regarding their wet traction. But, if you can afford them, the BFG All-Terrains are probably the most widely recommended A/T tire.
I don't mean to contradict myself... I'd buy another set of BFG's in a second. But the money I save from the Grabbers is going towards tune-up parts.