There are a LOT of hiking and biking trails in Portland. I would just do some research or buy a trail book at Powells. Also, I hope you like beer b/c the beer is literally amazing in Portland. Here's a few popular ones that come to mind.
For biking, there's the 40 mile loop, Forest Park for mountain biking, and Sauvie Island. For hiking, there's Forest Park, Multnomah Falls, and Mt Hood.