Fruit Ninja without any doubt. I don't care how simple the premise is, it is so well-executed and so mind-blowingly addictive that its worth ten times what I paid for it...
Back on topic Deadspace = the fun I had with this game its easily $10 game. I played this game like 4 times in different difficulty settings. The game is absolutely worth every penny. Spider SOBM= excellent use of iphone touch controls , what happened to the developer a part 2 should have come out 6-8 months ago Canabalt = just kidding haha
Driver - I got it on a free sale and it was one of the most fun games, driving especially, that I've had on my itouch. This is because I loved Midtown Madness on PC
Karnival-still the game thats been on my Touch the longest. Lego Harry Potter-for the sheer amount of gameplay. Angry Birds - though I rectified this a bit by buying the PC version for 4.99. Corporate Fury - Some of the most fun I've had playing a game.
Most games that I buy AND like... I always end up feeling it's worth more than price I paid. The max that I have paid for a game ever is 6$. And I have awesome games like Real Racing 1 and 2, a ton of Gameloft games, SF4, Jet Car Stunts, some awesome platformers like Soosiz and Bounce 1 and 2, a lot of casual games like Jump O'clock, Solipskier, grav runner, some cool dual stick shooters like Solomon's keep, Bug heroes... all these games are worth more than the price i got them for.