This is going to be less of a step-by-step tutorial and more a series of tips and a review of what I learned making my workbench.
After examining many, many workbench designs and almost settling on a German-style bench, I came across the 17th century French workbench of Andre Roubo. This design seemed to have surpassing versatility and an aesthetic superiority to every other design. In the construction process I learned of the trade-off between functionality, design, and ease of construction. I have made awkward-looking workbenches in one day which function perfectly. I've also made beautiful tables quickly and easily which are only useful as buffet tables. To make this workbench functional and attractive required that every surface be planed properly, and every corner be a perfect 90 degrees.
Step 1: Some Large Pieces of Wood
This style of bench begins with a few very large slabs of wood. The top and legs are each 5" thick to provide a simple shape with no joists or apron and the heavy stretchers provide ballast. The top is 72" long and only 20" deep. The narrow top discourages me from putting too many things on the bench at one time (treating it like a table, which it isn't) and the overall small dimensions are compensated for by the workholding features and dead weight. Holding down a heavy beam or large plywood sheet is no problem and the bench doesn't rock or scoot.
The legs and stretchers are reclaimed old growth Douglas fir. Though mine were salvaged (and thirty winters have hardened these beams nicely), here on the West coast, 6"x6" Douglas fir is a standard dimension. But finding a mass of wood for the top that's both deciduous and contiguous is a taller order. The top of a workbench should be hard. Exactly how hard depends on a few factors; if you're going to be working primarily with hard woods, then your bench should be hard enough to take some use but not so hard that it might mar the wood you're working. It's better to dent your bench than your workpiece. For my bench I opted for poplar wood, as it's harder than pine but still affordable (kind of). By happy coincidence I found a supplier selling it in 3 1/2" thicknesses*, which fits the leg joinery perfectly (the final beams were 3 1/2" x 5" x 72"). To keep costs down I used a reclaimed beam of glued-up Douglas fir for the middle 13" of the top. Since most of the work on a bench takes place around the edges I saved the hard wood for that area.
*My original intent for this project was to use only reclaimed wood I could get for free. Though I ended-up purchasing the poplar beams, I think sitting in my garage as long as they did before I completed this project qualifies them as reclaimed wood.