Depends upon the day of the week, how much you want to spend and where you are staying.
The Shilo Inn has a small lounge at their hotel near the airport. It is pretty good for near the airport, but it is small. I think they close at 11pm weekdays and midnight on Friday and Saturday.
http://www.shiloportlandrestaurant.com/lounge.html
There is El Gaucho Steak House in downtown Portland (SW); good steaks and a nice small lounge area. Good service but $$. I believe that they are open until 11pm during the week and midnight on Friday and Saturday.
http://www.elgaucho.com/El-Gaucho-Portland.html
Farther southwest (still in Portland) you have the Shilo Inn with The Mark Cigar Lounge. Much bigger lounge, lots of big-screens and full service food and drink. This tends to be a favorite of Stumptowners. 10pm Sun-Th, 11pm F-S.
http://themarkpdx.com/