Depends on what you use it for:
CardStar (store all those stupid store loyalty cards and scan your phones screen)
AroundMe
DataVault (paid, password manager)
Flipboard
Pocket (save to read for later service)
Amazon (great for price comparison in stores)
RedLaser (also great for price comparison)
GasBuddy (find lowest gas prices near you)
Starbucks (associate a gift card and scan your phone to pay to earn free drinks, etc)
Flight+ (for travel)
AutoSilent (set phone to silent/ring based on schedule so you don't accidentally ring during a meeting)
VIP Access (use your phone as a security token to log into paypal/ebay/your bank)
ShoeBoxed (store travel receipts for reimbursement)
Weather.com (way better than stock and get push severe weather alerts)
Remote (if you have Apple TV)
Your bank's app (most now allow depositing checks by taking a photo on your phone)