andfoot, I used rails and adjustable brackets. There are shelving brackets up to 18", mine are 11.5". Not sure why they are not 12" . This way you can adjust shelving height as things or moods change. I use medium density fiberboard for my shelves (1/2") and 3/4" for my work surface.
How ironic you should mention shelving...
I just finished cutting the steel to make the frame to finally add some shelving to the workbench I built last year. A friend is going to weld it up tomorrow, then I can drill for fasteners, and finally hit it with spray paint.
For the actual shelving, I'm using a similar adjustable setup, but found 16" deep, 3/4" thick laminated shelves (melamine on particle board). Will add 1"x1" steel angle to strengthen them up a bit to make sure it won't sag, even though it will have 3 brackets to support it. The angle will also add a lip so the equipment to help prevent me from knocking it off, as I'm a bit of a klutz (inner ear problems, trying to get it sorted).