Wow, it's hard to imagine that I've been using this workbench for three years. I'm writing this in November of 2000, and this bench is still sturdy, and as you can see from the photo above that I just took last night, it's covered in stuff! The workbench is in the basement, and it's one of two major centers for project work. The other is my office upstairs on the second floor.
I had found some plans for a 4ft. workbench in the local Home Depot, but I knew that four feet just wasn't enough workbench. I took a risk and doubled the plans. So far, it's worked out great, and I haven't ever regretted having the extra room. It has a shelf up top, and a shelf underneath where I store lumber and my big roll of Kraft paper.
The frame of the bench is made of simple two-by-fours in pine, held in place using these great metal brackets I bought at Home Depot. The maker of the brackets published the plans that I used, and I've recommended the plans and brackets to numerous people. The only thing about these brackets is that each three-way join of 2x4s needs something like a dozen screws to hold it together. Don't attempt a project like this one with out a power driver of some kind. It's also good to have a drill that is separate from the driver so you can drill pilot holes.
The upper shelf is an 8ft. board held up with more brackets. There's no bracket in the middle, so the shelf started sagging. I counteracted the sag by nailing a strip of 1x2 across the front of the shelf. This also keeps things from dancing off the front of the shelf as I hammer on the workbench surface.
The work surface and lower shelf are both Lauan plywood. The Lauan has a nice smooth surface, and isn't much more expensive than an equivalent thickness of regular plywood. It's plenty stained and scarred by now. If I'm trying to immobilze something for working on it, I tend to just screw it down to the work surface. I guess ebventually I'll have to replace the surface, but it's OK for a while yet.