For photography on the iPhone I recommend the following:

Flickr (if you have a Flickr account)
Photoshop.com (it's free)
CameraBag (a must have)
Lo Mob (great image effects)
Nikon Learn & Explore (free)
Camera Genius (pimp out your camera with added features)

Other apps I can highly recommend:
1Password (currently free)
Skype
Xing
LinkedIn (if you are already LinkedIn)
Tweetdeck (Twitter Client)
Bump (for exchanging info)
SBB Mobile (buy your tickets and get schedules on your phone)
iLingual German (a fun translator app)
Swiss Events (from mySwitzerland.com)
Wemlin (ZVV live timetable app)

I also use Facebook all the time, never had any problems.

Have fun,

Bryon Paul McCartney