I've had the Marmot Zephyr for a while now, and it's a good pack. Like many others, I never wear the hip strap while riding, only the sternum strap. Zephyr's got a bladder pouch and an airflow suspension frame (crucial).
Only negative IMO is that as handy as the back flap is for stuffing my jacket, scanners, cable boxes, other large items into... it has to be unclipped in order to easily load the main compartment.
Here's a link. I scored mine for $70. Make sure you try it on somewhere before you buy. Half the people who've tried mine on couldn't stand it.
http://marmot.com/fall_2008/equipmen...nfo/technology