Oh I missed this until today. If you want to rent a bike, there are plenty of places. If you want one to explore the city, Clever Cycles rents city bikes, complete with fenders so you'll be ok in the rain. If you want a road bike, I'd try Veloce or Pedal Bike Tours. Might be fun to do one of their tours too - I did one once as part of Pedalpalooza and it was well done.

Check out Rubber to the Road for some good routes if you want to do some rides outside of town. Riding to Multnomah Falls is something I really want to do one of these days. It's more like 65-75 miles round trip - 65 if you start at Mt. Tabor, so tack on some extra mileage if you're starting from downtown, though you could knock some off by taking the MAX out to Gresham first and starting from there. I've ridden the Columbia Scenic Highway out to the Vista House, but never all the way to the Falls. Someday!

Hope you have a great trip and enjoy your time here!