Though cool, I never really understood why he had to build several different suits. Why can't he just build one suit that has stealth, can go underwater or fly into space? I can understand building something like the WarMachine armor because that thing is equipped with all kinds of different weapons of mass destruction.
But seriously, building an armor that can fly into space and withstand high pressure shouldn't be big of a deal.
He does have a suit that can do all that - the Mark III. But any suit that is designed exclusively for spaceflight will be better at spaceflight than a suit designed to do it all. Wiki "specialization" if you need to.
...and for more toys.
That said, if the Mark IV is used for the last battle scene and destroyed at the end of the movie, and we have a return to the Mark III with some tweaks, for the credits, that would be kinda cool. Perhaps the Mark IV is the 'do it all' thing, eh?
Specialized Suits I'd like to see:
Silver Centurion (scene: Stark orbital laser satellite needs tuning/protection, perhaps in the opening scene)
War Machine (scene: Stark needs backup and Rhodey drops in with something hulk-buster sized and well armed, still grey and silver (not yet painted) )
Stealth (scene: Stark investigates Mandarin's operations, gets detected somehow)
I hope not to see random pointless suits... I always thought that was too much, and lets face it, there aren't hundreds of different environments to compensate for... there's barely half a dozen. "Underwater action" isn't really all that cool, imho. A sentient armor... that is, an armor 'piloted' by Jarvis could be pretty cool for a scene as a decoy, imho.