I would recommend at least one layer of 3/4" MDF either covered with hardboard or Formica, Though I think 2 layers would be better.
-Dan
My local Lowe's has 3/4" MDF for $24.12 according to the website. From memory Home depot is always a little more expensive, and Menards a little cheaper (here in Champaign IL anyway).
-Dan
If you are anything like me you will find that any flat surface in your shop will be used eventually as a place to bash on something. I'm just saying that making all horizontal surfaces as heavy duty as you can now will most likely be a good thing. MDF or ply, make it strong enough to clamp to and take future abuse.
Marc
Chuck,
Since I have the "real" workbench in the middle of the shop to do the heavy duty work, I used white laminate on my countertop over the side wall storage cabinets. I chose white to reflect light. I have a basement shop and wall mounted cabinets above the counter so it's a little dark along that wall. I will also be adding under-cabinet lights when I can find time to mount them. The top itself is MDF (3/4"+1/2" laminated together) a reuse of tops from old benches. Edges are wrapped in birch to match the birch ply in the cabinets. 1 1/4" tops are probably overkill but I like the weight of it. Really made for a solid worksurface. I extended the top about 3" beyond the front of the cabinet fronts to give me a clamping surface as well. Don't use it often but I still like having it.
Brian
I'm going to try an experiment of sorts. When a local Mervyn's closed down, I bought up a bunch of shelves from their store fixtures for something like 25 cents a square foot. It's 3/4 inch particleboard covered with a nice smooth impregnated paper finish. If that stuff doesn't work out, I'll replace it with some solid core doors I have, but I think it will be fine for countertops. I also have a 4 foot length of butcher block countertop I'll use somewhere.
I picked up a home made workbench for free that's working out well as an assembly table until I can build something better.