Pokemon Red & Blue. I got both of these games as a Christmas gift from my grandma plus a Pokemon Game Boy Colour. I played Red more than Blue, thus, Red is all beaten up and Blue is in great condition. I later started choosing a version later on. (Silver, then Crystal, then Sapphire, then FireRed, and then Emerald) I later got LeafGreen after I lost FireRed. :/
I got into the GameCube and bought Colosseum and rented XD. I eventually bought XD and beat both versions with ease. (I used 2 Umbreons :p)
When Diamond & Pearl came out, I decided to buy both of them, but got more into Diamond and gave my Mom Pearl (She is a die-hard Pokemon fan) I bought Platinum, then Soulsilver, then Black, then Black 2. And finally, I bought X. :D
Now, don't get me started on the other Pokemon games (Trozei, Dash, Channel, Rumble, etc...)