There aren't really any apps other than Graal that have me super addicted. However, cube runner is pretty fun if you ever played that on the computer. I'll see if I can name some more later.
i enjoy Canabalt. it's good for useless fun
I'd have to say that N.O.V.A 2 is an ok game too, too many hackers tho, so its only fun if you cheat yourself
Jetpack joyride, GraalOnlineClassic, GraalOnline Era, doINK (if you want a simple iPad animating program), Scriblenaughts, 7 little words, Stick Wars, iRemote ( Allows you control a computer iTunes library from iDevice)
Make sure you get an app called "App Deals". It will show daily new free and price cut apps each day and you'll recognize a lot of the apps on there on some days.