The best radio interface available for controlling 433MHz devices is in my opinion the Tellstick Duo. Unfortunately this device is not sold in the US/Canada. So to have something that is possible to use there, I have added support for the JeeLink classic. JeeLink is an Arduino compatible programmable radio transmitter/receiver sold by JeeLabs/Digital Smarties. I have developed a small firmware for JeeLink that allows it to act as a generic 433MHz transmitter for OpenNetHome. It does unfortunately not support reception, but on the other hand it is quite inexpensive (€32.50).
To use it, you have to install the OpenNetHome firmware on it, see this page for more instructions. Support is implemented in the nightly build.