Have you checked out the Oregon Gator blades? They have a pretty good rep of being a top quality blade. Unfortunately while I was working on my Brother-in-law's John Deere mower, there weren't any Gators in stock at the store. So I ended up going with Arnold Xtreme blade, which are kind of a knockoff of the Gator. He absolutely loves the way it mows now.
L8R,
Matt