One of the future projects I am working on is an Arduino variant based around Atmel's new Atmega128RFA1. This chip is an Atmega128 core with a 802.15.4 radio onboard. This allows it to function as a Zigbee node. I've provisionally called this new board the Zigduino.
I ordered one of the dev kits from Digikey, and I now have it in hand and have an Arduino bootloader ported over. Next step is porting over enough of the core libraries to generate a non-trivial sketch. I should be receiving the first prototype boards next Friday (21 May 2010); I do not know when I'm going to receive my first chips. The date keeps getting pushed out -- current estimate is that they ship from Atmel to Digikey on 20 May, but we will see.