None of those are really special or hidden, well the ships and balloons, those have been around for a few FS releases already.
But i did read a while ago in the Flightsim forums about hidden things in FS, like have you seen what Microsoft's headquarters look like (well i haven't but it's supposed to be good). You can also see the first powered flight at Kitty Hawk by the Wright brothers, if you set the date back to 1909 and go to the right place (i actually saw a screen shot of this).
Also there's lots of places that have fireworks at certain times, and in FS98 you could actually see the olympic flame in Atlanta at the 96 olympics. So stuff like that is what you might wanna look for, you never know you might even catch a space shuttle launch if you're lucky.
.... and if you wanna see more ships, take a flight through the Panama Canal, it's littered with cruise ships and things.... well it was in FS2000.