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!
433MHz radio technology has been around so long, it's become ubiquitous and inexpensive. A great example of this is the Wicked Devices Receiver Shield kit. Pair this up with your own Arduino and a Wicked Node kit for a range up to 300' (we have tested it at more than that line of sight).
It is extremely simple to assemble and use, the kit includes the board, radio receiver, antenna, wire and headers.
Instructions for assembly are available at http://receivershield.wickeddevice.com/