Des Moines off Redondo Beach has a nice place. Alki Beach I believe has a small area too or Gasworks Park. The weather has been nice, so you can rent tables and chairs and hire a caterer. If you are interested in Filipino food, I actually cater myself.
Check out golden gardens bath house - it's right on the beach!
Here's there info: http://www.seattle.gov/parks/reservations/rental_brochure.pdf
Click on each tool to see a sample.