Throw this bundle together to have one of the first Arduino-compatible Mini-Sumo kits out there. Get your trusty soldering iron out, build the Sumovore and Sumoshield Kits, then toss the Arduino on-top, program it with the supplied code, and watch the Sumo/Line-following madness ensue.
This Arduino shield rocks a socket for wireless modules, such as Digi Xbee, so that you can float your bits and bytes of data through air with the greatest of ease.
SparkFun has mounted a RFM22 433MHz ISM FSK transceiver module to a shield. What's it do? Let you do a cheap point-to-point (and basic mesh networks) using 433MHz!
Want to do some wireless communication for the Arduino, but on the cheap? The Wicked Devices 433MHz Receiver Shield will give your Arduino-compatible ears!
You want to move power? We've got the SeeedStudio Relay Shield that'll let the milliamperes of an Arduino-compatible board to control up to 35VDC 70W on 4 separate channels!
Yes, there are other music/mp3 shield out there, but SEEEDStudio does it again with a very complete unit!