http://www.eabco.com/KA-BAR.html
Visit the above link to see what the US Marines are being issued as a bayonet. I have one and trust me, they are nothing to get misty eyed over. I can think of no better weapon than 7" of cold steel when you are out of ammo and in close combat.
My Dad made a knife out of an old Lawnmower blade. The blade itself was 10" long. He somehow tempered it so that is held a nice hard edge. The first 4 inches of the blade was double edged with the upper edge slightly concave (reverse curve).