Although not directed at me--it depends on the style, how much you want to pay, etc.
Camille Fournet, ABP, and a craftsman I saw an article on recently, Hughes Handcrafted, all make excellent straps. I only have experience with the first two, but the latter I have heard good things about!
If you want some less expensive options, check out Hirsch. They make straps at various price-points.