kgault, welcome to PNW diving! Unlike most people, you are actually coming when the tides aren't bad. This means that there are some nice sites that are easily accessible to you, and more, if you can hook up with someone local as a guide.
For unguided diving (and assuming you will be in the city of Seattle for your business, rather than some other place) I'd recommend the Edmonds Underwater Park. It's a shallow dive site (max depth 40 feet) and has an excellent map on the end of the restroom building, to help you get oriented. There is a rope grid system in place, to help with navigation (which is basically west outbound, east inbound, anyway). Although there is not the variety of life you can see in some of our more challenging sites, there's plenty to interest someone who isn't familiar with our water, including some of the largest ling cod you will see ANYWHERE!
Another good site, and very close to downtown, is SeaCrest Park (otherwise known as the Coves at Alki). SeaCrest Cove 2 is a very popular place, and good site maps are available on line (check out pnwscuba.com). The navigation is a little more complex than Edmonds, but depth contours are very helpful. We frequently see Giant Pacific Octopuses here, in addition to many other local species. This is a site where you shouldn't have any problem at all finding someone to dive with you -- but it's also a site where a great deal of training takes place, so diving it on weekend mornings is not optimal.
For a night dive, Redondo Beach (again, refer to pnwscuba.com) is a fantastic site. I have routinely seen multiple small octopuses, stubby squid, market squid (although this is not the season for them) many varieties of gunnel, sailfin sculpins, a few rockfish and of course, our varieties of anemones and other sessile life. Depending on your schedule, NW Grateful Diver might be able to join you for a dive there -- he lives nearby.
Unfortunately, I work the last two days of July and the first day of August, so I won't be around to play hostess -- otherwise, I'd be delighted to do that.
As far as charter boats go, the only one I know of out of Seattle proper is the Aluminator. It's a small boat; and it looks as though it's been chartered by Seattle Scuba Schools for that weekend. But you could always contact them and see if there are any empty spaces. The Bandito charter runs out of Tacoma, and they run a very good boat. With tides as they are, you should be able to hit some excellent sites that weekend. There are also charter boats that run out of Anacortes to the San Juan Islands.
I hope you have a good visit -- and I hope you hit one of our windows of better viz. Our summer viz has been pretty bad!
