Step 1: Get the Parts
1. Glue: I used Titebond #3 Ultimate wood glue
2. Clamps: it can be done with 2 clamps, I used 24" Jorgesen clamps (#3724). Irwin clamps are also pretty good.
3. Wood! The most important part by far. Since this is a board that is going to have knives hitting it fairly regularly, using a hard wood is important. I used seven 2x2x20" red oak boards from Home Depot, who cut the boards to length for you. I think Loews has comparable wood. If you want a more expensive wood, walnut would work as well. Hard maple also looks very nice, and is considerably cheaper. I choose oak because that's what the local store had that day. The boards I got cost $40 altogether.
Note: Do not use tropical wood, as some people have allergic reactions to them. I personally have never seen this happen, but I have heard of it from two different people.
4. A decent power sander. This is helpful for smoothing the sides, top and bottom of the board after gluing. You can do this by hand using a sanding block, but it will take some time/effort.
5. A hand plane. You're going to need this to level the ends of the board, as the rough cut pieces of timber are not going to be exactly to length.
In addition to the above, a level work bench with good lighting and a wet cloth for wiping away excess glue are very helpful to have.
Step 2: Glue the Board
Once you have the boards arranged the way you like its time to glue! Starting from one end of the board, place a line of glue on one side of each connection. In other words, between the first and second strip there should only be one side with glue on it. Go though each strip in this fashion, pushing the sides together as soon as the glue is applied. Make sure the ends of the boards line up as close as possible, since this will save time sanding later. After all the board are glued, clamp tightly, placing a clamp about 1/3 of the way along the long side of you cutting board as in the picture. Its a good idea to place some scrap wood between the clamps and the board, since this will distribute the force from the clamps evenly as well as protecting the board from dents/scratches.
Tighten down the clamps until the lines between the boards are almost gone (ie very tight). Wipe away the extra glue, and let sit for 24 hours. Make sure the temperature stays above 55 degrees Fahrenheit since wood glue generally wont cure if its too cold.
Step 3: Sand and Plane the Board
After the board is smoothed to your satisfaction, start on the short ends. Its possible that the wood pieces are close enough is size to avoid planing, in my case I had to use a hand planar to level the ends. Try to use a planar made for crossgrain work. I used an old cheap box plane because that's all I have. If you have a power sander to cleanup the scratches after the boards are level it doesn't really matter what kind of plane you use.