This JeeNode wireless communication platform looks like a fun and cost effective way to get into experimenting with RF communication. By combining an Arduino-compatible processor (ATmega328) with a low-cost HopeRF radio module, they were able to make a tiny, fairly well featured kit with wireless capability. They are offering them for sale as a kit, or, since it is an open source hardware design, you can just download the PCB layout and roll your own. I can think of lots of applications (remote candle lighter, interactive cat toy) that aren’t worth a full xBee-based solution, where it would be handy to have a development board like this that I could just drop in and use.
JeeNode, a low cost wireless sensor node