If above average sunshine is a requirement, I'd say your search should be limited to Southern Idaho. Major cites are Boise area, Twin Falls, Pocatello, and Idaho Falls.
Of these, I think Pocatello fits the best, it is drier than Boise, but closer to ski resorts, etc. and more moderate housing prices. I found some data on days of sunshine up through 2002, but it only has Boise and Pocatello in Idaho, tied at 64% sunshine.
Sunshine- Average Percent (%) Possible (http://www.ncdc.noaa.gov/ol/climate/online/ccd/avgsun.html - broken link)
Spokane, WA (close to N. Idaho came in on this at 54%)
The city data pages actually have some data on sunshine, Here's Pocatello
//pics2.city-data.com/w6/sun4970.png (broken link)
Pocatello, Idaho (ID) Detailed Profile - relocation, real estate, travel, jobs, hospitals, schools, crime, news, sex offenders
most of southern idaho looks similar, but you can compare from here.
Idaho Bigger Cities (over 6000 residents)
Click on the cities and scroll down.
Klamath Falls, Oregon also boast a number of days of sunshine, but southern and eastern Oregon is also a drier climate, similar to southern Idaho.