Unless you have different rear rims than stock, or plan on replacing them with your tire purchase, you are going to be severely limited in selection.
I just went through this with my sons Blaster that I bought for him for Christmas. There are only 2 or 3 options for the stock rear rims.
I chose Kenda Kutter XCs for the rear, but had to buy new rims with the tire purchase, so overall, it wasn't cheap.
Pretty sick tires, though......they got very good reviews, are 6 ply, and the lugs on these things are pretty savage.
If you're replacing just the fronts, (21x7-10), you have a ton of options.