I had a great experience with Gallery Frames in Pioneer Square (it was recommended to me by the Davidson Gallery). They framed two large prints for me and did a nice job.
I used to go to Queen Anne Museum Quality Framing back when I worked up there. Not too far from Belltown. Quality work and they have great reviews online.
When I lived in Belltown, I only went to Innervisions in the U District. Yes, it's a tiny bit out of the way, but you'll thank yourself later. Anne and the crew are wonderful. It got to the point where I would just drop something off and let them decide on the frame. Reasonably priced, and high quality. freshchalk.com/innervisions...
I have heard of two places artist friends of mine use regularly. One is Plasteel Frames on 1st Ave South, and the other is Dick Blick framing services on Capitol Hill. Blick often has framing services sales too, so it may be more reasonably priced. I have seen both results and they look great, although I've never used either personally. plasteelframes.com dickblick.com/stores/custom...