Thanks to Drew for sharing! Check out TCPoke here.
TCPoke is a collection of projects that allow you to connect your Game Boy, Game Boy Pocket, Game Boy Color, or Game Boy Advance to the internet and trade or battle with the first(Red, Blue, Yellow) and second(Silver, Gold, Crystal) generation Pokemon games.
At the core is a Teensy 2.0 shield and accompanying firmware to connect the Game Boy to a PC over USB. Then there is a lobby client that you can use to set up a connection to another player.