Seattle, King County, Washington, USA June 13, 2009 Size: approx 25mm
Found nectaring at Garden Sage, Salvia officinalis.
I'm thinking perhaps Bombus fervidus. Went to the Bumble Bees of the World web page and did a search based on color patterns (http://www.nhm.ac.uk/research-curation/research/projects/bombus/index.html) and came up with B. fervidus.