Canon 50D has a Canon EF/EF-S lens mount and currently there are 333 native lenses available for this mount.
The latest released lenses that are compatible with the 50D are the Carl Zeiss Makro-Planar T2/50, the Tokina 35mm f2.8 Macro DX and the Canon 50mm f2.5 Macro.
Canon 50D doesn't have a sensor based image stabilization system but
113 of these lenses already comes with optical image stabilization.
Since Canon 50D has a APS-C sensor, it has a focal length multiplier of 1.6× so you have to multiply lenses original focal length with this multiplier to find the Full Frame equivalent focal length of the lens when mounted on 50D.
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Canon 50D Lenses with Image Stabilization
Canon 50D Lenses with Weather Sealings