The EFX-Tek RS-485 adapter is an ideal solution for putting multiple microcontrollers on a custom network.
The Prop Plug is a compact USB to Serial connector for microcontroller programming and communication. We're about the best place in the universe to get them!
Ever need a convenient way to log 4 channels remotely, and don't have a lot of time to mess around programming up your own? PICAXE to the rescue!
Just need to make some motors move with your Arduino? Here's a simple way from SparkFun - the Ardumoto!
The Voice Shield™ (VS) is an analog audio shield for the Arduino that allows you to play audio sound byte.
This is a 7-segment shield for Arduino NG/Diecimila/Duemilanove and many Freeduino boards.