I have a Duffco Enterprises (
www.duffcoenterprises.com) prerunner bumper on my 99. Their standard bumper is made out of 1.5" x .090" wall thickness round steel tubing. For $100 more, I had them make mine out of .120" wall thickness for a little bit of added strength. I then had a local welder custom fabricate some support braces on each end and a stronger mounting bracket that allows it to bolt up to the stock tow hook bolt holes underneath each frame (as well as the front frame bolt holes where the frame horns sit).
This setup has worked well and saved my truck from some serious front end damage. I hit the other side of a ditch head on at about 35-40 mph. The bumper held up and there was no front end damage (it then rolled on its side, though, and caused some body damage in that respect, but the bumper did its job).
One good thing about round steel tubing with .120" wall thickness is that it is strong enough to protect the front end, but it is also "soft" enough to bend a bit and absorb the impact. The bumper bent about 1/4" to 1/2" upon impact. I couldn't really tell it had bent at first until I looked at it from the top. This is exactly what I wanted to happen in the event of a head on impact against an immovable object (which in this case was solid packed earth) - instead of the frame crumpling, the bumper bent a bit, but not enough to cause any front end damage (radiator, grill, and stuff like that).
Their bumper also comes with a 1/4" thick aluminum skid plate and 2 light tabs (no damage to my Hella 500 lights, either). I highly recommend Duffco's prerunner bumper made out of .120" wall thickness and reinforced with some custom mounting brackets and support braces.