actually XBee module has 7 analog/digital I/O + 1 digital input + 1 digital output + 2 PWM.
If you are planning to use it for simple sensors condition transfer you don't need any additional MCU connected to XBee module - you can do it by simply configuring module itself.
Actually XBee HAS integrated MCU - MC9S08GT60, and this is PROGRAMMABLE - you can take SDK for customization of XBee there:
http://www.maxstream.net/products/xbee/xbee-oem-rf-module-zigbee.php
(XBee Code Development)