Definitely gives The Rickshaw a run for the money.
Update: Now that I know that Amber from Go Like Hell, touring with the Genitorturers, etc. etc. works there (and easily clinches the most sexy bartender title), I have to boost this over the Rickshaw for top Seattle karaoke dive and to my highly recommended list.
Historical Notes: The "Arterial Tavern" begins appearing in city guides at this address in 1939 and it is listed as the "Crescent Tavern" in the 1948. It is said to have been an old carriage house, although the current building wasn't constructed until 1924. It was a lesbian bar by the early 70s and now caters to older gay men, with a broad mix for karaoke.
seattle weekly - yelp - the stranger