Best Activities for Kids in the Seattle Area? [SURVEY]

I'll be in Seattle next week for a family vacation. If you were me, where would YOU take the kids? We know about the Pacific Science Center, the Space Needle, the Gum Wall... where else?

Our kids range in ages from infant to teen so I need suggestions for all ages. We've been saving up, so we can spend money, but we're a big family, so frugal suggestions are welcome. What are your favorite parks? Anywhere a few minutes north or south of Seattle worth the drive?