I Have em ALL!!! Call me the gadget geek!
For what your desribing as your needs, I think the forerunner 305 is your best bet.
You can easily switch from biking to running mode.
Running hubby uses the forerunner on his bike, but I have an edge so I don't need to. I use it strictly for running. Oh- and I have the 200 series of both because I don't use a hrm.

Now speaking of gadgets, has anyone seen the 705 (or is that 605) that has a power meter option??? SWEET!