Found it somewhere on the internet so I haven't designed them by myself. I just recolored them.

The blue and the metal slime are the original ones. I just resized them to be a bit bigger.
In the bottom there is a hole so you can make a pile of slimes :)
http://img834.imageshack.us/img834/2817/orangeslime.png [orange]
http://img856.imageshack.us/img856/8789/metalslime.png [metal]
http://img830.imageshack.us/img830/7752/greenslime.png [green]
http://img98.imageshack.us/img98/3291/blueslime.png[blue]