I recently participated in an omnibus order for some Tiny TX4 433 Mhz sensor nodes. They were primarily designed by Nathan Chantrell to be compatible with OpenEnergyMonitor, Nanodes and Jeenodes.
The nodes use the Atmel ATtiny84 microprocessor and a HopeRF RFM12B transceiver module. Thus, they can be programmed using the Arduino IDE. They can be easily used with a DS18B20 digital temperature sensor, a dual temperature/humidity sensor, such as the DHT22 or an analogue temperature sensor such as the TMP36 or many other kinds of sensors.
They are powered using three AAA 1.5 V batteries. Thanks to some modifications, including a booster and the power-saving ATtiny84-PU microcontroller, battery life is now extended up to one year.
The receiver communicates with the Raspberry Pi though it’s serial port. Transmitted data can be recorded to a MySQL database by listening to the serial port using a simple Python script.
This open source project is very well documented in the German Raspberry Pi Forum where you can possibly sign-up for the next omnibus order. Arduino sketches and the PCB layout (Eagle-Files) can be obtained from github.