I'm not a big tourer or anything, but I have a friend in Salem that I would like to ride my Surly Pacer to go and see. So, I assume plenty of people have done this ride before. What routes do you take?

Tabor,
Try mapmyride.com (I searched for Portland, OR with keyword 'Salem' and got 7 routes). Here is the corresponding link.
http://www.mapmyride.com/search?txtPageNumber=2&txtSortBy=featured_flag+desc%2C+average_rating+desc%2C+route_name&txtLocation=Portland%2C+OR&txtKeyword=Salem&lstRouteTypeID=2&btnSearch=SEARCH+%3E

Thanks!

Just did this last Saturday. 99/Barbur to Newberg, take the 219 south. Beautiful country, plenty of shoulder, not too many cars, virtually no hills. A great ride except that I've run into fairly strong headwinds every time I've gone this route.

I assume you are starting at Mt. Tabor.
You can ride south on the 205 path, now under construction and easily stay on 99E or find lesser traffic roads near there. I went to Champoeg park a couple of times from Tabor that way, on the east side of I-5 the Canby-Marquam Hwy looks pretty good, if you go west of I-5 you can take 219.
Good riding.
Paolo

Thanks everyone! Cyclerclyde's route is the closest to the one that I was looking at. For this journey I would actually be starting in SW Portland near Beaverton.