Cascade and Commons for more unique beers. You can go to any corner and get a good IPA.
This!
Spent six weeks in Portland this summer and went to both of these multiple times....
You can take the light rail, Max, south from the convention center area and easily hit Commons, Cascade Barrel House, and Base Camp, which are all within walking distance. Also, Green Dragon and Loyal Legion are nearby and have lots of taps. Hair of the Dog is a little farther south and west, but not far.
I have to respectfully disagree with McMenamin's- generally nice, historic, locations but with bad service and lackluster beer. I'd hit every other brewery in town before them. Especially as a tourist looking to sample Portland beer.
Also, if you go north and west by bike or transit you can easily hit Upright near the Rose Garden; plus Widmer (for big breweries), and Labrewatory and Ex Novo just up the hill on Russell.
I agree on McMenamins.....it's meh, in my opinion....and avoid Lucky Lab. They don't seem to clean their beer lines very often and the beers were gross.
Cascade and Commons are musts...
Base Camp is good, but be careful getting there....lots of homeless camps have popped up around there.
In that part of town, I also enjoyed Grixsen (a bit south of there but easy to get to via bus, and relatively new, but good beers and nice atmosphere). Also, Baerlic is pretty good and on the bus line to Grixsen.
Imperial Bottle Shop has some nice offerings as well, and occasionally some Russian River stuff on tap or in bottle.
If you go to Green Dragon, ask what's on tap 19. It's usually not on their list, but it is often something desirable (like Pliny).
Burnside, Migration, and Culmination are all a long walk frim the Convention Center, and all pretty good.
Gigantic is a bus ride to the south, but worth the trip.
Ecliptic (to the North) was good I thought...the head brewer developed many popular beer recipes when he worked at Full Sail and Deschutes earlier in his career.
Breakside SE is hard to get to via mass transit, but a great place.
If you can get a car, check out Bent Shovel out towards Oregon City. Tiny place (basically on a small ranch), but good beers. Hit Drinking Horse on the way there, or back, if you go.