I have the Edge 705 with speed, cadence, heart rate and an altimeter. The altimeter is a plus over GPS grade / elevation data since it provides accurate numbers. Also, the 705 has the ANT + protocol which means that it can read power from power meters that support the standard which is the principal reason I opted for the 705.
I plan on getting a Quark crank based power meter once the sensor is available for compact cranks. Projected availability is January 2009.