If you're building several Arduino/XBee devices, you might take a look at the Stalker V2 + enclosure from Seeed Studio:
http://www.seeedstudio.com/depot/seeeduino-stalker-v2-p-727.html?cPath=80
http://www.seeedstudio.com/depot/seeeduino-stalker-v2-enclosure-p-734.html?cPath=178_184
Very nice devices, RTC + SD Card + XBee socket built in, LIPO charge/interface with solar charge capability built in, shield compatible, etc. I've purchased several and am quite happy with them.