any bluetooth mouse and keyboard usually will work without an app, ive got 4 of each in my paired devices, and all logitech, but they work
airdroid, yes, +1
nova launcher or zeam, i just want full screen with low thrills
easytether, usb tethering, its working great for me
netflix and crackle, now both apps are still a bit buggy, and you have to uncheck "do not kill activities" in system settings/developers options all the way at the bottom, efore they start working better.
dolphin browser hd, again, full screen thing
dropbox and google drive!
gStrings guitar tuner,

and
samsung apps, Photo Editor, i dont know why ut i like it alot etter then anything on the market.
cant forget words with friends and square card reader app!
stay away from facebook app, buggy and troublsome, just use your browser or friendcaster. no task killers/battery savers, pretty much useless on this phone.