Currently there are 28 native Macro Prime lenses for Canon 50D and 22 of these lenses are autofocus (AF) type.
Canon 50D doesn't have a sensor based image stabilization system but 7 of these Macro Prime lenses features optical image stabilization.
Since Canon 50D has environmental sealings (Weather Sealing), you may like to couple your camera with one of these 7 Macro Prime lenses with Weather Sealings.