A website that you can arrange a bedroom on line?

I'm looking to re-arrange my bedroom around, to maximize what little room I have, and my bed it huge, and it's hard to mentally arrange the room in my head to see what is the best arrangment. Is there a website, that you can like enter the mesurement of a room, and maybe map out your current arrangement of the room, with the size of the furniture, and then allow you to arrange the furniture online or thru a program and tweak it around until you find a good layout?

I'm sure there is some program out there, that designers use, but I'm just looking for a basic free service that offers this, just so I know the best way to arrange everything.

Thanks a ton!