More types of dragons.
And no, I know what you're going to say...http://skyrim.nexusmods.com/downloads/file.php?id=3829. But no, this is not what i'm talking about. I'm not just talking about dragons with different skins and/or different attacks. Nono. I'm talking about different SPECIES of dragons.
http://images.wikia.com/metroid/images/5/50/Ridley_zerom.jpg/http://www.draconika.com/img/red-dragon.jpg dragons, http://www.quiztron.com/quiz_images/full_153991716.jpg, http://mythologyandlegends.webs.com/photos/Mythological/Chinese_Dragon2.jpg, http://fc08.deviantart.net/fs19/f/2007/273/6/d/Neo_vs_Three_Headed_Dragon_by_XUnlimited.png (These would be ESPECIALLY badass, imagine 3 or more heads throwing shouts at you at once!!), That sort of thing. Actual VARIATIONS of dragons instead of just the wyvern-variety dragons we have now.
That would not only add to the game somewhat, but it would open up quite a few possibilities for modding.

