Any electricians available? Wire size question...
If you want to have both 110 and 220 volt service (or only 110 service), you need to run 4 wires from the panel to your shop (the 2 110 legs, a neutral and a ground), but if you want only 220 service you can get by with only 3 wires (you can omit the neutral).
I am going to guess that you will probably get something like 2 gauge. Buy it by the spool at Home Depot or Lowe's. That is much cheaper, on a per-foot basis, than buying smaller amounts. The problem is that you'd have to run 2-gauge in an underground plastic conduit. That's what I had to wind up doing.