I've been thinking about this myself. From the east side, there are good routes to go east (Marine Drive, Springwater), southeast (Springwater), or south (Oaks Bottom-17th-River Road). When you start trying to go west, it gets harder.
Terwilliger is very nice to ride on, and is a fairly decent grade. I am told that the city is looking at ways to make Capitol Highway more bike friendly, which would take you from Hillsdale to Barbur. That's not a bad way to go.
Another option might be to go up through Riverview Cemetery, and then find your way along Taylor's Ferry road. That gets all your climbing out of the way up front, but I don't think Taylor's Ferry is too friendly. There might be some good side streets around there, though.