Notes Section
A page to save notes, memos, or reminders, (kind of like the field on the main page of Airline Empires) to oneself in-game would be pretty amazing for some.
I float between playing this game on my desktop and laptop, and once I return to back/commuting I will be using my netbook as well. When playing AE I frequently would leave notes to myself about where I was putting new aircraft when they came in, new routes I wanted to add in the future, etc. I'm sure not everyone uses multiple devices to access the game, but for those who do, it would be a much appreciated and hopefully easy add-on to implement!
I don't know that if I would recommend putting it on the "main page" or the game or not, I would think it would be better suited under "manage airline". You could even have fun with it and say it's tied in with the executives and/or corporate operations. It could be entitled "internal mail" or "internal communications".