if you go out toward the fire training academy on I90 towards snoqualmie pass, get off there (exit 38), follow the road east till it goes under the freeway and to a bridge. find the mark on the west side of the bridge- marks the deepest spot.
highway 2 at eagle falls (near baring). swim across river to a little scramble up. You can get jumps from around 30-60ft there.
Banks lake (a bit far) but has a lot of options there.
If you hike up to Lake Serene (on mt. index) there are some good options on the west side of the lake. Nice deep, clear, and cold water