Don't buy normal trousers belts, instead buy elastic belts which can last literally for life
(i5.walmartimages.com)
I've heard good things about NAB Leather, but have no personal experience.
What you want is single-piece full-grain leather about 10-12 oz weight. (This is a leather thickness measurement, not the weight of the belt.)
I find that trade shows (e.g, home/garden shows) often have a few vendors who make top quality belts.