KLM has a good sale on their nonstop flights to Amsterdam from Los Angeles and San Francisco with tickets priced as low as $444 round trip. Departure dates are February and March, then October and November for prices in mid-$400s.
Delta and Air France offer one-stop tickets for about $5 to $20 more round trip.
KLM Los Angeles LAX – Amsterdam AMS – LAX
KLM San Francisco SFO – Amsterdam AMS – SFO