Pokemon: Ruby Version
Welcome to the beautiful region of Hoenn, home of all sorts of interesting people, places, and Pokemon: Ruby Version. It's up to you to explore the region and see if you can find, capture, and train over 200 different types of Pokemon. Of course to do it, you'll also need Pokemon: Sapphire Version.
Pokemon: Ruby Version is almost the exact same game as Pokemon: Sapphire Version except for a few minor changes. In fact, the ONLY changes I saw between Sapphire Version and Ruby Version are the title screen graphics and some different Pokemon. Like the older Pokemon 'color'? games you'll need to link up both versions of the game (which, of course, requires an additional GBA, link cable, and another cartridge) and do some trading to collect all of the different kinds of Pokemon available.
With that in mind, unless you're a hard core Pokemon trainer you'll likely only need one or the other version of this game to get most of the experience out of it. Just find a friend with the other version and you're all set.