Here's a neat HopeRF RFM69CW radio module breakout board. An affordable choice to add modern wireless capability to your Arduino (original or compatible).
Supporting both 5V and 3.3V power, this matches a whole range of Arduino (original or compatible) boards. Upgrade Freeduino, JeeNode SMD kit, RBBB, Boarduino and many others with an effective wireless link. For clarity, the header pins are labeled with the Arduino specific pin numbers as well as the actual signal names. Just plug into your MPU board to enable remote signalling, control and sensor acquisition.
The RFM69CW modules can't tolerate 5V power directly. This board features a step-down voltage regulator and resistive voltage level converters on the key signal pins. With a 3.3V supply, leave the regulator and level conversion components off the PCB. The RF module mounts directly on the pads provided (only moderate soldering skills required - google for some great tutorials & hints).
N.B.: An antenna must be connected to the module - extended operation without a matching antenna at the higher transmitter power levels risks permanent damage to the RF module output stages. A quarter wavelength, 82 mm wire works well (included).
The Kit 868 MHz variant includes the optional parts needed for power and level conversion, a tested RFM69CW radio module tuned for the 868 MHz ISM band, an 8-pin header and flying leads. Solder everything on to upgrade your Arduino (compatible) board to wireless.
The Kit 433 MHz variant of this kit is tuned for the 433 MHz ISM band. Chose this version if you are interfacing to other equipment that uses this band , such as weather stations.
The PCB-only version is just the plain board. No parts, no headers, no RF module. If you need the RF module in a 3.3V setting, you can select this option - just add the C2/C3 decoupling capacitors and a RFM69CW 868MHz module.
For multi-node networks, try the 6Pack or Bonus Packs - that's 11 pieces for less than the price of 10.
The drivers, examples, documentation and full design details are freely available.