I've been using Shimano MTB shoes with Shimano SPD's. I just got a pair of clearance priced ($20) Specialized road shoes, with SPDs. However, the SPD cleat itself is a different size than that on my mountain shoe, and didn't fit. So for about $18 I bought a pair of Shimano replacement cleats for the road shoes. Now when I need to do a lot of walking I can use the MTB shoes, and if I'm just riding a long way I'll use the road shoes. Much cheaper and easier than buying new pedals.