According to this unwieldy Flash map, Jake the Alligator Man is Washington's biggest tourist trap. Who is Jake? He's a half-man, half-alligator on display at Marsh's Free Museum in Long Beach and a former Weekly World News cover boy.
Whether you agree with this assessment probably depends on how you define "tourist trap." To me, its the inescapable, billboard-every-five-miles attraction that seems more prevalent in the South and Midwest. To others, it might include anywhere a visitor and his money can be parted. (In which case, wouldn't the Space Needle be our state's biggest tourist swindler?)
Either way, there's no consensus answer to the question, as even an informal poll of Daily Weekly's offices revealed a host of potential candidates, including the waterfront's Ye Olde Curiosity Shoppe, the Aplets & Cotlets candy factory in Cashmere or roadside zoo Olympic Game Farm.