It depends a lot on your budget, but for me, either a nice normal trophy, an engraved picture frame, or a fitted cooler/ blanket/ quarter sheet in the size of my choice would all be good prizes. I actually would kind of like a belt buckle, too, as long as it wasn’t gigantic, but I’m not sure if that would appeal to a lot of English riders.
Probably my most used prizes are a fleece vest with the association logo, and a big duffel bag that is perfect for putting pads/ blankets etc in for shows. One thing I would definitely never choose is a glass trophy-- I have one and I am afraid to even display it for fear my cats will get it.