The newer Forerunners (including the 305) are compatible with the chainstay wheel/cadence sensors that the Edge series uses, and you can set them up with different settings for three sports (bike, run, "other"), so you can definitely use them on the bike.

I'm holding out for the Forerunner 310XT that's supposed to be released next month, to replace my old Forerunner 301 that's starting to wig out on me. The 310 has the same size display as the 301 and 305, but in a smaller case (among other upgrades).

I don't know what kind of handlebar mount it'll take though. You definitely don't want the 301 on your wrist while cycling, it's too big and too hard to look at.