For the actual pad that you hit, the cymbal, can be any sort of trigger. For the pedal, some shops bundle the SamplePad Pro with these cheapo keyboard pedals that can be set to variable or switch - in this case we'd want to use Variable, so that the hihat can progress from closed to open gradually.
For that, any trigger pedal will work, but just like the previous comment, the DMHat pedal is recommended as a good one, and I tend to agree.