Raj of Embedded Lab has written up documentation on his Si7005 breakout board:
The Si7005 is a digital relative humidity and temperature sensor from Silicon Labs. It integrates fully factory-calibrated humidity and temperature sensor elements with an analog to digital converter, signal processing and an I2C host interface in a single monolithic CMOS sensor IC. The Si7005 is available in a “non hand-assembly-friendly” 4×4 mm QFN package, which requires reflow soldering to mount it on a PCB. This breadboard friendly breakout board is designed to make your prototype project with the Si7005 sensor much easier. It can be used with PIC, Arduino, or any other microcontroller development platform through an I2C bus. The power supply and I2C signal pins are accessible through breadboard friendly 0.1″ pitch header pins. Note that the Si7005 sensor is not 5.0V tolerant. It must be operated at 2.1-3.6V power supply.