I highly recommend the Puget Sound Guitar Workshop, near Seattle. Not just for guitarists (though that's certainly an emphasis), there's singing, dancing, and instruction in other acoustic instruments as well. The student concert is a unique experience--four or five hours of music, and nobody wants to miss a minute. And what the site says about the strength of the camp being its teachers--I heartily agree. The staff makes a concerted effort to hire faculty who are not only excellent musicians but also excellent teachers. You won't be disappointed. I haven't been there since 1990, but would dearly love to return some time. (I did finally make it back to Camp Harmony this year, so maybe PSGW will happen, too.)

Aloha,
Mark