SW Portland to Wilsonville
I've got family in Wilsonville, so I do this one occasionally. It might be pretty obvious to most. You stay on bike lanes almost the whole way. The only major hill is 99. Wilsonville is a nice town for biking too.
-99W heading SW
-Left on Hall Blvd
-Left on Durham
-Right on Boones Ferry
Following Boones will take you into N. Wilsonville. From there you can take 95th to Boeckman which will get you to the east side of I-5, or continue south on Boones Ferry, right along I-5. You also have access to the WES stop.
Instead of 95th you can take the country route and go on Grahams Ferry to get to the southern part of WVille. This also passes through Villebois.