Unlocked phone buying advice

Fellow Verge-ers: I need to buy an unlocked, and preferably unbranded, phone for overseas travel (mostly in Asia and Africa). My desired specs are (in rough order of importance):

  • No more than around $400
  • 3.5-4.3 screen size
  • Good camera
  • Offline maps, either built in or as an additional app purchase is fine
  • Reasonably durable
  • Decent battery life

I am OS agnostic - I currently use WP7 and iOS (iPad) but have used Android, Symbian, and Blackberry as well. I'd prefer to stay away from BB and Symbian (though could be convinced otherwise) and would like a reasonably clear upgrade path to ICS if an Android device.

I have looked at the Nokia N8, but it is Symbian. I can also find the Arc S for just over $400 online, but I am worried about its durability and how it will run ICS when that is released in a couple of months. I have also thought of an off-contract iPhone 3GS, but the camera is a bit weak. Any other phones I should look at, or thoughts on the N8/Arc S?

I'd appreciate all recommendations.