Small design that includes Arduino, XBee socket, Li-Ion battery jack and USB charger for it. I'm jumping ahead in my understanding but had to try this.
SparkFun Electronics - Funnel IO
funnel.cc | Main / HomePage
funnel.cc | Hardware / FIO (Funnel I/O)
Xbee Adapter - wireless Arduino programming
Arduino Forum - Yet another small size Arduino clone with XBee
Arduino Forum - Simple Xbee passthrough with SoftSerial