What bracing is appropriate for this shelving?
I agree, you should use some "L" shelf brackets UNDER the shelves to the vertical supports. There are many you can chose from, but even the cheap gray 10 inch ones would work fine. Remember, if you use 3 supports, the load is divided, so each bracket will only be holding apx 1/2 of the load resting between two supports.  If you mount them over the shelf, rather than under the shelf, the load will be supported only by the mounting screws rather than transferring the load to the upright post, for that reason, I'd stick with mounting them under the shelf.  Your shelf as pictured without braces will most likely split at the line where the mounting screws are, as the grain of the wood follows that direction.

BTW, nice workbench!  Good luck