Lake Washington and Lake Sammamish are both pretty good lakes with better boat ramps. Lake Washington has ramps on every end of the lake. If you go out on either watch the weather if you go very far from the ramp. Both can get pretty choppy if the wind picks up and lots of boats are out.

This is a good link to find boat ramps.

http://www.iac.wa.gov/maps/default.asp
_________________________
Wear a PFD if you want to live.