I have an alarm clock that has a "bed shaker" that is just a large vibrating puck you put under your mattress. (i am very very hard to wake up but with the bed shaker thing going i wake up pretty fast and im not too annoyed by it after i wake) i was actually very surprised by how violent it vibrated, the puck would bounce around my table wen i was testing it out. it does have a regular audio alarm that supposedly gets extremely annoying and loud very quick, but you can turn that function off wile still having the bed shaker work. i found it on thinkgeek.com, im sure u can find it elsewhere
ThinkGeek :: Sonic Bomb Alarm Clock with Bed Shaker
ThinkGeek :: Sonic Bomb Alarm Clock with Bed Shaker