The lakes listed by others are excellent,if I was to toss in another option,it would be Alder Lake.
This time of the year isn't to great,they lower the lake for flood control but from mid spring to fall,the lake is at full pool
and offers some excellent fishing for kokes,trout,large and smallmouth bass. You can camp and moor at the Alder Lake campground on the west end(near the dam) this campground is operated by Tacoma Power,along with Rocky Point,a few miles further east. If my memory serves me right,I believe boat mooring is operated on a "first come,first served"basis.
If you have family and/or friends and want to take a break from fishing,checkout the Mount Rainier Scenic Railway in Elbe.
If your into off roading,there is also the Elbe Hills ORV Trails located between Elbe and Ashford.
As jens stated,Riffe is another one. I really enjoy camping at Taidnapam(east end of the lake) There is also the Mossyrock
campground. Both are also operated by Tacoma Power,clean and well maintained but I don't care for camping at Mossyrock,the tent sites are WAY to close together. Basically,if your neighbor snors or eats some beans....you will know.