I am going to build a sensor network composed by some Arduino Fio that will collect some data and send it to a RaspberryPi.
After a little research it seems that XBee would be a good choice for the communication between the Fios and the RaspberryPi.
Do you recommend any XBee hardware for the RaspberryPi?
I am actually building something which sounds identical to what you are trying to do. Its part of my final year project at University. I have not released the codebase yet, but the github repository maybe worth bookmarking for later :) I'll be releasing in about a months time. At that point I'll have detailed information about what I used in the construction.
In the mean time take a look at the shopping list that I put together to get started, it may give you some ideas:
2 x Raspberry Pi Model B
2 x Polymer Lithium Ion Battery - 2000mAh
6 x Solar Panel 1 Watt
2 x Arduino Fio
1 x USB to Serial TTL Cable (OEM FTDI Cable)
1 x XBee Explorer USB
2 x One Wire Digital Temperature Sensor - DS18B20
2 x Barometric Pressure Sensor - BMP085 Breakout
2 x Xbee 2mW Module with Whip Antenna (Series ZB)
1 x XBee 2mW Module with Chip Antenna (Series ZB)
