There aren't a lot of options for the Montero Sport. Also the lifts are different between 1997-1999 and 2000+. 97-99 used leaf springs in the rear and 2000+ used coil springs, so you have to be more specific on that first.
I have a 2" Old Man Emu (OME) lift kit on my 2000 Montero Sport and am very happy with it. It's is very inexpensive and is good quality. There are some new options available from Adventure Driven Design (ADD) you should check out too. But I don't think anyone makes more than a 2" suspension lift off the shelf for these trucks. If you want to go higher than that you would need to do an additional body lift. I'll post some pictures and links to help you out.
Looking at your profile you have a 2002 so I'll focus on the coil spring rear. you have coils in the rear and torsion bars in the front. The coils in the rear are replaced with stiffer springs to lift the rear of the truck. In the front the torsion bars are tightened, causing the front to lift up. Then all 4 shocks are replaced.
Check out OME kits here:
http://www.rocky-road.com/mitsubishi-montero-lift-kit.html
Check out ADD kits here:
http://adventuredrivendesign.com/ocart/index.php?route=product/category&path=71_76
And here is a before and after picture on my 2000 Montero Sport. The top picture is factory sagging suspension with 245/75R16 (30.4" diameter) all terrain tires. The bottom picture is with the 2" OME kit and 255/85R16 (33.1" diameter) all terrain tires.