I'd suggest Wamu and First Tech.
Wamu's quite far away from the convention center, about a mile and a half at the Fred Meyer on Broadway, or in front of Pioneer Courthouse Square down the MAX line. I learned the hard way that they don't have anything within walking distance of Lloyd Center. That was mainly why I wanted to take on this project
First Tech, however, appears to have some ATMs really close. If you bank with First Tech Credit Union or any other Credit Union or other Co-op that is part of the
Co-op Network you have several choices that are really close.
I might as well post the addresses now, since I looked them up.
Electra Central Credit Union
825 NE Multnomah
Portland, OR 97232
and
650 NE Holladay
Portland, OR 97232
Portland Teachers' Credit Union
1720 NE 9th Ave
Portland, OR 97212
I excluded the ones that are restricted access since those buildings will probably be closed on weekends. But I'll try to drive around and confirm everything after I've generated a list.
And Washington Mutual:
3030 NE WEIDLER ST
PORTLAND, OR 97232
and
811 SW 6TH AVE
PORTLAND, OR 97204
Wamu's site also lists an ATM location I've never been able to find and don't believe actually exists, but if anyone can find it, they say it's at Lloyd Cinemas, across the park from the hotel. I would not count on that location at the con, as I have personally attempted to locate it to much frustration and no avail.