I only disagree with Zari about going into Powell's if you are broke. Sure, you can easily spend a good amount of that rent money (esp. since there's often a markup on books). But you can also not spend money there in several ways:
1) for the price of a coffee, hang around in the coffee spot and read all those books you don't really need, but have to read.
2) read those books in the aisles! great way to meet people, too!
3) Play the Powell's scavenger hunt: leave your phone number, or a favourite quote, in various books in each colour-coded room. Either wait for phone call, or just let it be. Or, look for what other people have left... try to find the links between books.
4) Make money by bringing those books filling too much room in your bathroom (or that evil housemate's collection) in for cash/trade.
Powell's has a great zine section, but the best place in Portland for zines is Reading Frenzy.