Great places in Portland for micro-brew beer enthusiast?

I would add a couple things to hannah's answer Horse Brass Pub is english style pub and posts an impressive beer list. Also, while not local, Yard House has over 120 beers on tap and I believe around 40 are local. For a smaller vibe with some good beers on tap but in bottles too check out Saraveza and Concordia Ale House another impressive beer and bottle list. 

There are so many!

I must admit, I haven't been to Loyal Legion Pub yet but it boast 99 Oregon beers on tap. Essentially, a beer lovers dream. A short drive away is APEX with 50 beers on tap (Oregon and otherwise). While they don't serve food they allow you to bring your own food there. There is a Taqueria Los Gorditos right next door that you can grab a burrito from. If you like garlic get extra orange sauce. 

Breakside Brewery is always trying new and exciting things. You can settle in with their Sunshine Pilsner or get a sampler of some of their more experimental brews. 

If you want to stick to a clustered area Mississippi has some nice offerings. You can start at Ecliptic Brewing for a pint and an expensive but delicious burger, get a taster at StormBreaker Brewing then top off your night at Prost! (German beer served in traditional glasses). If burgers aren't your thing, Radar Restaurant and Interurban have tasty food as well.

Enjoy your trip to Portland!

Just outside of Portland is Mcmenamins.

I recommend the Green Dragon Bistro and Pub. It has a very solid selection of beers from around the region.

If you can make the trip to Astoria, you won't regret going to Fort George Brewery. Their tap list is wide and varied. Still the best spruce ale I've ever had.