Total Gen 5 typing list (in order of most to least):
Grass: 20 (2 two-stage families, 6 one-stage families, 1 basic, 1 legend)
Flying: 18 (1 two-stage family, 5 one-stage families, 2 basic, 3 legends)
Bug: 18 (2 two-stage families, 5 one-stage families, 1 basic, 1 legend)
Normal: 17 (2 two-stage families, 4 one-stage families, 2 basic, 1 legend)
Water: 17 (2 two-stage families, 4 one-stage families, 2 basic, 1 legend)
Dark: 16 (2 two-stage families, 5 one-stage families)
Fighting: 15 (1 two-stage family, 2 one-stage families, 2 counterparts, 2 evo-gained types, 4 legends)
Fire: 15 (2 two-stage families, 3 one-stage families, 1 basic, 2 legends)
Psychic: 15 (2 two-stage families, 3 one-stage families, 1 basic, 2 legends)
Steel: 12 (1 two-stage family, 2 one-stage families, 2 evo-gained types, 1 base, 2 legends)
Electric: 11 (1 two-stage family, 2 one-stage families, 2 basic, 2 legends)
Rock: 10 (1 two-stage families, 3 one-stage families, 1 legend)
Dragon: 10 (2 two-stage families, 1 basic, 3 legends)
Ground: 9 (1 two-stage family, 2 one-stage families, 1 basic, 1 legend)
Ghost: 9 (1 two-stage family, 3 one-stage families)
Ice: 7 (1 two-stage family, 1 one-stage family, 1 basic, 1 legend)
Poison: 7 (1 two-stage family, 2 one-stage families)
I'm pretty confident that I didn't miss any, but I made this list partially for my own reference, and partially because I was curious. Someone has probably already made a list like this (probably in this thread even, it took me a little while), but this is pretty much idiot-proof in my opinion xD