A lot of people (like myself) are still waiting to get there hands on an actual R-Pi, and there are people also waiting for the Gertboard.
For anyone lucky enough to all ready have a pi (or that just cant wait) and interested in playing with the GPIO's, I'd like to introduce the "Slice of Pi" from Ciseco plc.
This is a simple GPIO breakout board with prototyping area and an XBee style connector.
The Xbee style connector is great as it quickly allow people to get stuck in adding wireless sensors & projects straight onto the Pi via the Serial UART.
Most Xbee shaped devices like the XRF / XBee / RN-XV / XBT / RF-BEE etc run at 3.3v and so don't need any logic level conversion to use with the R-Pi
And of course XRF/XBee's have been used to talk to Arduino and other micros already so there is plenty of example code out there.
As soon as I get my R-Pi I'll be working on some examples using XRF's with various sensors and will try to post back here.
The Slice of Pi is already available to buy from the Ciseco web-store http://shop.ciseco.co.uk/slice-of-pi/