Check out Edmonds Underwater Park. About 45 minutes away, but a pretty cool low key dive.
EUP is about 1.5 hours from Tacoma, depending on traffic. It is an amazing dive, but a long haul and the traffic can be a nightmere, especially on a Friday. However, there are tons of sites in the Tacoma area.
Les Davis is about the closest to the convention center (about 10 minutes). This is such a fun dive. Tons to see, easy access and restrooms right there.
However, there are some great little sites in and around the area too.
Redondo is about 30 minutes north. As Bob said, it is a great shore dive and lots to see.
Dickman Mill is on the waterfront too. Shallow dive and the pilling are pretty cool to poke around.
Fox Island West Wall is about 25 minutes across the bridge. Great site to see an octo.
Sunside is a flat, easy dive about 25 minutes away in Steilicoom.
Dane and the daily diving gang are checking out a new site this evening. I will post information once they dive it. It is also very close by.
If you are more experienced, there are a couple of deep dives I can recommend as well.
Some of the preimere sites, like Titlow, Sunrise and Day Island are close and fabulous, but not a great weekend to dive them due to the tides.
Don't forget about the Treasure Hunt on Saturday morning at Owen Beach. If you don't have a buddy, they will find one for you.
If you are sticking around until Monday, Rick said he could put together a charter then. PM me if you are interested.