I second SJI Sailor's Pacific Power recommendation.
Both Pacific Power and Coastal Marine are very well regarded in Seattle and both are Volvo Penta dealers / authorized repair shops. However, Coastal's estimate for annual maintenance was about 40% more than Pacific Power for the same work, including the travel time expense. The labor rates were comparable but Pacific Power can (and did) say they would get it done in much less time, which was actually much more in line with the number of hours I'd expect (Coastal Marine quoted me more hours than it would take me to get the job done myself!)
Pacific Power quoted me roughly the same hours as the Volvo dealer in Bellingham, who I also quoted for comparison (labor rates in Bellingham are cheaper too, so you can always decide to take a trip! Though the fuel will cost you). So it did seem like Coastal was padding a bit, unfortunately.
So, YMMV -- I would get quotes from each -- but I'm sold on Pacific Power.