I tried the Lite version of Moon Drop and I'm already impressed. I'm baffled by the poor ratings this game has gotten. Now on to try the PP Lite version...
Wow, I just tried the 'Parachute Panic' Lite version and I love it as well. It seems to have many more obstacles and enemies to the game than 'Moon Drop' does. I really like the simplicity of 'Moon Drop' though. Hmm...this will be a tough decision...
Leaf Bound. Like Doodle Jump but with more character and bosses. It's different in a few ways... I prefer it. Also the obvious free games, Jelly Car, rRootage, Trace, Pocket Tanks and MazeFinger are all worth playing if you haven't already. If you like puzzle games, my favourites are PathPix, Cookie Drop (best looking 2D game on the iPhone!*) and Electric Box. *personal opinion.
Saucelifter is a great pick up and play shooter. Westbang is another really addicting p.u.n.p. game. Try the lites.
Get Parachute Panic and Moon Drop. Also, Bluebird is fun. Harbor Master is sooooooooo much better than FC
Moto X Mayhem (.99), fun trying to shave seconds off the courses. EDIT: Also, Guinness World Records (.99) is full of little mini-games to keep you occupied.
harbor master, papi jump, icopter, zombievile usa, Ouch!... Sky burger!!!! there's a plethora of games like these
No one mentioned G.I. Joyride yet? Because in all honesty, that game's been the best pick-up-and-play game I have ever played in my entire life. As well, it's about to get a major update to make it more awesome.
I've had 'G.I.' Joyride for a while now and it's a very entertaining game. The update will make it ten times better.
G.I. Joyride is a blast, all around. I find The Magic Blackboard is great for short (and not-so-short) play sessions. Arctic Shuffle (and it's sequel) are both great. Peggle is fun (and very addictive) BaDaBoo is also good to kill a few minutes...