Pokémon Fire Red and Leaf Green, they were my very first Pokémon games, they aren't the original cartridges I owned, I had lost those over the years, but like 8 or 9 years ago I purchased them again. I'm pretty sure they still work but I haven't checked because I don't have a charger for my Gameboy SP at the moment.
The oldest one I own that is my original copy is Pokémon Platinum, and yes it still works