The APC220 is a convenient quick solution for wireless serial communication. The 40$ package contains two modules and one USB -> TTL converter (for connecting to a computer’s USB port). I used it in my Bot in a Box for communication with my laptop. It claims to be able to transmit at 1km at 9600 bps (line of sight), but I haven’t tested that yet. Long story short, I think it’s perfect for the Arduino. In the Arduino IDE, it can be treated as a normal serial connection. It also uses only 4 pins (by default): VCC, GRND, RX, and TX, only two of which need to be connected to the microcontroller.
As great and as easy as it seemed, I had problems with my modules that made me ditch them for two years. Only now do I realize what I had done wrong. In the APC220 setup software, the Net ID must be the same on both modules but the Node ID must be different. The mistake I did was to write the same settings to both modules, thinking that both should be configured the same way. Anyways, here are some good links to getting started with the APC220:
https://www.robotshop.com/content/PDF/dfrobot-apc220-manual.pdf
http://fritzing.org/projects/wireless-arduino-with-apc220
Link down: http://wiki.openpilot.org/display/Doc/APC220+Transceiver+Telemetry
Cached version: https://web.archive.org/web/20140905180839/https://wiki.openpilot.org/display/Doc/APC220+Transceiver+Telemetry
