The little back water on the Clackamas that the Sheriff moors their boat in has panfish and bass - it's sheltered from the wind pretty well. Access via Clackamette Park and walk upstream, you'll see the place.
Across the river, hike down to the water from MS Young Park in West Linn - it's a pretty good hike down from the parking area, mostly on paved trail, but then the trail gives way to a dirt path that pops you out near the rocks. Good smallmouth fishing around there in warmer months. Walk down stream, cross the foot bridge onto Cedar Island, follow the path through the little thicket of woods, and fish the lagoon. LM Bass, SM Bass, crappie, carp, and panfish galore in there.
You might also try driving out into farm country off of HWY 99 toward Canby/Hubbard - and see if you can't sweet talk some land owners into letting you fish their ponds. Lots of ponds visible from the roadways...
Aside from that - I'd wait until the water and the weather warms up a bit, then hit up the Willy's backwaters near Hwy 99, or cross the river and fish the Tualatin.
Panfish will eat just about any fly you throw at them - if you find them in shallow water, my favorite methods are a size 10-12 dry fly - something bushy and high riding - or a size 12 popper. If the fish are holding deeper, micro buggers or traditional, bright colored wets are my favs.