Hey man. You can do so much with a pad. I really like having the double pedal practice pad and my HQ pad on a snare stand. With that setup you can really get into some great excercises. Same goes for single pedal.
Aside from rudiments you could check out some snare drum solo's. Wilcoxon's 150 is a great book. The pad is a great place to work on hand technique. For example; Moeller Method, Push/Pull, Finger/Wrist Isolation to name a few. Get creative with it. Work on varying your metronome interpretation (hear the clicks as &'s or E's and A's). For more of a workout you can layer towels on top of your pad. Start with one and see how it feels to add more ect.
Hope that gives you a few ideas. Pads are great. Just remember to relax that grip and try not to absorb the shock of the stick into your hand. You can damage your wrists with bad technique that way (on most pads).