for productive use:
urbanspoon - finds great restaurants...lived in columbus for years and it picks ones I never knew of
chase bank - handy for keeping an eye on Chase

balance - handy mobile checkbook, great for keeping track of expenses a certain bank (cough) takes days to post/posts in incorrect order
flixter - linked reviews to rotten tomatoes now, and you can buy tickets
chipotle - duh
red laser (amazing) - finds deals on pretty much anything with a UPC, and handy links to online ordering too
myWireless - great to monitor data/min. usage, pay bill as well
for fun:
TALKING CARL...halarious

...says anything you say, and you can poke him haha. my little nephew loves it
facebook - stalking is mobile...yesssss
backdrops - amazing pics from interfacelift.com, best background app IMO
iFart - halarious named farts...you can even record your own (gross). also you can set a fart, leave the phone, and the next person who touches it activates the sensor and it goes off. dont this many times