I just bought a second bike and want to put pedals on it that are compatible with with my SPD shoes so that I use the same shoes for both bikes. Looking on e-bay, there are lots of different Shimano SPD pedals but it is not clear if they all use the same cleat. That is my question. The pedals I am using now are PD M-505s

M505s are the bottom of the SPD line. I would look for M520s as they are a better quality pedal. Any Shimano SPD pedal will use the same cleat. I'd stay away from the knock-offs as I've yet to find one that is as well made as the Shimano pedals and the few cents saved will most likely soon be forgotten. Not sure what you are looking to spend but Pro Bike Kit has the M520s in black, white or silver at $41 a set with free shipping. As you go up the line, the pedals get better but, IMHO, the M520s are the best value.