It depends upon where you are going to be.
1. Timber Valley** in Beaverton (SW of Portland)
2. Paul's in Beaverton
3. Rich's** in Downtown Portland
4. Broadway Cigars in SE Portland (check out their website
http://broadwaycigar.com/).
** Not sure of you can smoke in these shops (due to state laws)
There is also The Mark cigar lounge at the Shilo Inn in Portland (border of Beaverton and Portland). The Mark opens at 3pm daily.
If you want to spend some money El Gaucho steak house (downtown) has a cigar lounge. They open at 5pm.