Flashlight app. Obvious reasons.
Someone already posted Whatsapp which is effecient as fukk for putting sms on the back burner.
Quickpic- if you have and save tons of photos and pictures off the net like myself, the stock image browser won't cut it. Quickpic is fast and reliable and don't crash as much as the stock browser or any other that I've seen.
Flixster - I don't watch alot of telly or read Entertainment news so I'm always in the dark on new movies. But it's one thing I like to do when I'm in America or abroad is show up to the theatre and watch random movies on a whim. Flixster gives you a broad range of what's in theatres, reviews and trailers. There is an IMDB app I'm sure, but Flixster works fine enough for me.
XE Currency exchange app - So I can know when dap a store clerk after buying a European beer or shove the rest of the Kroner he gave me after looking to stiff me on my change down his swarthy throat.
Kindle app - Use it in conjunction with some free book services in my email. It pretty much turns your phone into a kindle so you can use it without having to buy any iteration of them things if you don't want one, since you already have a capable smart phone and all. Plus the free one off books can be interesting time wasters if your a voracious reader like myself. Works well with Amazon Prime too since you get a selection of free books each month for the service.
Pink Pad - It's an ovulation tracker.

Now I'm a dude through and through but you ever been dating a female and you can't remember her cycle or how any of that icky girlstuff work? Have her make an entry, set it up so you can know when to hold her and when best to tie her to a chair and feed her chocolate 'cause she's on the rag.
BsPlayer Free - While VLC is king on the PC, BsPlayer Free works better in my opinion from interface to the ability to skip forward or backward without having to move the little dot on the time line, to searching instantly for subtitles when you catch the Internet. shyt's awesome.