Take the Zeiss Planar f/2 Macro, add USM and you have the perfect 50mm
Actually, however, if you put USM on the Planar f/1.4 the result would still be quite impressive. Would be an absolute best-seller.
Both of them are on the expensive side, though not really as much as the Canon L counterpart.
Another amazing best-seller would be the Sigma, if they could resolve a bit of the field curvature issue that spoils the game quite a bit in terms of edge sharpness. It's already a quite good lens though, on a APS-C I would prefer it everyday to the Canon.