Is a gun belt necessary? Does a bear, uh, live in the woods?
I don't do IWB, so I don't know how critical a good belt is for that. But for OWB carry (as with many other things), a good stiff belt can help!
I think just as important as the belt's stiffness (with leather this is usually achieved with a double thickness) is the belt's
width. I like a 1.75" belt, which still fits in the loops of most jeans or work pants. For dress trousers, you can use a narrower belt or have your belt loops made bigger.
A lot of guys here seem to swear by The Beltman, but I get my leather belts from
Bob Mernickle,
http://www.mernickleholsters.com/pb/pb7.html
Figure on paying $100 or so. I think it's worth it. His belts are way heavier than even the Bianchi and Safariland belts I used to use, and those were nothin' to sneeze at!
I would also advise that, for concealment, go for plain leather, no "Lazy 8" stitch or basketweave; those kind of shout "pistolero".
I used to know detective-types who would wear their buckle on the side, presenting only leather from the front view, on the theory that a shiny buckle made a target in low light. But if you're carrying a holster
and a couple of spare mags, a buckle on the side is just going to get in the way. But I still wouldn't go for a big, shiny "rodeo" buckle. But that's just me.
For hot weather wear (to avoid perspiration damage to leather), or just to go cheaper than leather, a fabric belt from
Wilderness Tactical or
5.11 works just fine (I use one with a fabric holster from
WRB). Once again, get the stiffest belt (with a stiffening layer inside), preferably in 1.75" width. That should only set you back around $30 for the 5.11, although the Wilderness can be twice that.
Don't skimp on a belt; a good one is a wise investment.