That for your suggestions guys/gals.

there are actually 2 apps called gStrings. One helps you tune your guitar. the other is a Chippendales calendar.

.Google Play store. If you have Android, some devices don't have it pre-installed
.Subway maps, if you are going to travel to larger cities. They are just off-line images
.Tripadvisor. If you don't have a VPN, it can act as an alternative to 4square for locating businesses and sightseeing spots around you
.PPTV. After you create an account, you can download films and TV shows (on wifi) and watch them off-line. Good for killing time on the plane. If your device has HDMI, you can also get an HDMI cable (50rmb) and watch the films on your TV while it's streaming on your device. Plug and play.
.McDonald's coupons. If you don't care about diabetes or heart attacks, it's an app that loads coupon images for discounted McD (and other fast food) meals. To save bandwidth, load the images on wifi and just present the one you want to the waiter. The icon of the app is blue with a yellow "1"

Here's a good site for Android apps:
search.liqucn.com/[...]

If you have a jb'd iPhone, go to Appaddict for your apps. DL direct to iPhone and they have everything.

CityMaps2Go is a great GPS app. You download great city maps all over China and then no need for data connection to use it.

Any conversion app is very handy here.I use one called Units.

ANother on I use a lot is Builders Helper. Very powerful builders calculator.

The best cam app is KitCam.

IDPhoto is good to have a handy way to quickly print out perfect ID photos for visas, passports, etc.

WeChat is very cool. I'm not into social media stiff, but this one can be used like a walkie talkie to talk for free to anywhere in the world. Way better than Skype.

Flightboard actually takes realtime data for all airport Arrival/Departure screens. Know what is going on in real time with your flight scheds.

Currencies is the BEST converter around. Bar none.

iPhone Apps
QQ - Spammy (is that a word?)
SKYPE - gotta love free international voice & video calls with virtually ZERO spam.
WIFI Analyzer - how busy is your wifi immersed environment (geeky)
Scany - scan a class C (250+ IP addresses) including ports (super geeky)
Remote VNC - control your mac or PC from your iPhone.

If someone hasn't mentioned it, DongDong for the iphone. Great for train schedules and can even check how many tickets are left per class. Available in english.