I looked up the city boundaries of Portland, Beaverton, Tigard, and Oregon City - those cities in the greater Portland Metro Area with a 'No Loaded Open Carry' law on the books and approximated them using Microsoft MapPoint 2009. I had to use the 'Census' level data in order to get some of the boundaries even close (ZIP codes were too generous) and even so, this map is not entirely correct.
It does, however, give a pretty good feel on where you cannot carry openly without a CHL in the greater Portland Metro.
The only other three cities of I know of that restrict carry are Salem (no surprise), Dallas, and, ironically, Independence. Those are all closer to the Salem Metro area, so, if I have time, I'll try to whip up a map for that later.
IANAL - don't rely on this to keep you out of trouble - it's just a basic visual guide. I hope it's helpful.
P.S. - Note Milwaukie, Oregon, where we're having our meet this Thursday, is right in the belly of the beast.