Plate Curl
The jump in difficulty between plate sizes is very large, so progression in the plate curl is typically achieved by affixing additional small weights to the plate until the wrist gets strong enough to move up to the next level. A couple of pony clamps or c clamps work well for this. Moving the added weight further out on the edge of the plate will make the exercise harder.
Due to the stress placed on the wrists, it makes sense to gradually work up the weight on this exercise. Starting with a 10lb plate, make the first target 2 10lb plates clamped together. Try to progress to a 25lb plate for reps. Plate curling a 35lb plate is attainable, but will prove to be a very challenging goal for most.