I use a crossbreed supertuck for my USP 40. I love it. Before getting the supertuck I couldn't carry it comfortably.
But don't stop at the holster. I believe a holster is only as good as the belt you are carrying it on so make sure you get a good gun belt. The USP is heavy and if your belt isn't designed for carrying heavy objects you will not carry it comfortably. I like the Wilderness Instructor Belt, but you can find other options for dressier wear if that is more your taste.