ios and mediaserverd
The mediaserverd daemon/process handles almost all (audio and video) media in iOS, so to answer your question, there is a long list of supported media formats/types for iOS 5.0.1 on Apple's website: http://www.apple.com/iphone/specs.html. There haven't been any significant changes to this list since iPhoneOS 3. Mediaserverd mostly encodes/decodes media, so the player may differ, but the core process does not.