Hardware
See ChoosingAnXBee for help deciding which series XBee is best for your project
XBee 804.15.4 Models http://www.digi.com/products/wireless-wired-embedded-solutions/zigbee-rf-modules/point-multipoint-rfmodules/xbee-series1-module#models (recommended)
- XBee 804.15.4 Wire Antenna http://www.digikey.com/product-detail/en/XB24-AWI-001/XB24-AWI-001-ND/935965
- XBee Pro 804.15.4 Wire Antenna http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=XBP24-AWI-001-ND
XBee ZB Models http://www.digi.com/products/wireless-wired-embedded-solutions/zigbee-rf-modules/zigbee-mesh-module/xbee-zb-module#models
- XBee ZB Wire Antenna http://www.digikey.com/scripts/dksearch/dksus.dll?vendor=0&keywords=XB24-Z7WIT-004
- XBee Pro ZB S2B Wire Antenna http://www.digikey.com/product-detail/en/XBP24BZ7WIT-004/602-1181-ND/2344902
The XBee Explorer USB is the easiest device for connecting an XBee to your computer. You can also find these on ebay for much less, but keep in mind delivery will often be much slower and they may not be ROHS compliant. It took 10 days for mine to arrive from China (I'm in the US). Note: You will need to solder headers to the board if you want to access Reset or I/O pins.
The simplest way to hookup a remote XBee is with a XBee Explorer Regulated This board exposes the XBee's IO pins and regulates power to 3.3V. According to the website you can provide up to 16V power supply to power the board.
The Arduino XBee Shield is the easiest method for interfacing an XBee to an Arduino. There are lots of different shields available. Again, these can be found on ebay from China at lower cost.
Series 2 radios require firmware update to work with this software (API mode) since they always come from the factory with AT firmware. Firmware is updated with the X-CTU application; it is only is available for Windows (I run it on VMWare on Mac). It's not required but often a good idea to upgrade the firmware on Series 1 radios as they often ship with old firmware.
See XBee Firmware release information for all radios for more details http://www.digi.com/support/kbase/kbaseresultdetl?id=2209