Check out the website for Cascade Bicycle Club. They have a lot of organized rides -- different locations & abilities. Also a great resource for general information and bike advocacy.

I keep meaning to try out one of their rides, but have been too busy/sick/anti-social.

A lot of new office buildings have secure bicycle parking for bike commuters.

Recreationally, there are some great trails. You might be able to look up the Seattle City Bike Routes map online. I use it all the time to make up my own rides.