I run a lot as well as bike so I bought a Garmin 310XT. It simply unclips from my wristband and onto my bike mount when I'm doing a biathlon or duathlon. It has an HRM and a built in GPS and I enjoy downloading and looking at the data and maps of where I have run/biked. I have the cadence sensor on my bike so it displays actual, max and avg cadence too. It will also display power if I buy an Ant+ compatible power meter.
'08 Fuji Roubaix RC; '07 Schwinn Le Tour GS; '92 Diamond Back Ascent EX
I've got the wired version of the Cateye Strada w/ cadence and it has been great. Very small but I can still read it. I especially like that it mounts to the stem and the pick-ups are both on the chain stay so the wires run down the down tube and aren't too annoying. I'd like to go for the wireless version but can't justify it since the wired one works so well.