DS: 5 (Feel the Magic, Polarium, NSMB, Mario Kart DS, Advanced Wars DS)
GCN: 15 (I don't care to list them)
SNES, Genesis, N64, and NES: back at home, and I've bought so many used that I never even played that I couldn't begin to tell you how many I've got. I think the only one that might have fewer games than GCN is N64, though.