I can't believe they left this out of the controls menu. I found out how to drop an item on the Internet, but can't find how to sit. Please help.

To sit on a chair or bench you simply activate it, as you would a door. You cannot sit on the ground in this game.

EDIT:

http://www.nexusmods.com/oblivion/mods/5243/? gives you a cushion activator you can place wherever you want, allowing your character to sit on ledges and rock you would not ordinarily be able to sit on.

http://www.nexusmods.com/oblivion/mods/6239/? allows you access to NPC animations, including a kneeling pose.

OK, thanks!