http://moderndevice.com/product/sht21-humidity-and-temp-sensor/

http://www.miniinthebox.com/fr/fc-28-d-sol-module-de-detection-de-hygrometre-capteur-d-humidite-du-sol-bleu_p685424.html

http://hardkernel.com/main/products/prdt_info.php?g_code=G140264897696 Weather Board en i2c 20€