MAX light rail is fantastic. it'll take you within walking distance to probably 70% of the city. very cheap to (something like $2.50 a ride if I remember right).
if you have a car you have tons of hiking opportunities. if not, tryon creek state park and hoyt aboretum are within city limits. also washington park, pittock mansion make sense to visit if you're up in that area
lots of breweries.
gays love the pearl district (just north of Old Town).
tourists like Vodoo Donuts. wierd-ass donut flavor combinations.
Jimmy Mack's is cool if you're into live music (jazz) although it's really not that hard to find open mic's or live gigs at many bars around the city.
if you're going to be working out there (and i'm guessing by the looks of you, you are).. LA fitness and 24 Hr fit are the two main club chains
if you want to visit some hipster stores/coffee shops, try hawthorne blvd.