RFM12 is a transmitter and receiver module in single board. It can be powered by using 2.2V to 5.4. it makes ideal module for embedded systems. Module communicates via SPI interface.
Wigbert Picht and Dirk Milewski have made simple Atmega8 tesboard, where RFM12 module is soldered as SMD element and can be configured with jumpers. There can be any sensors connected to this board like temperature. Schematic and sample Bascom AVR program are available for download.