British Airways offer some great solution to various US West Coast cities when departing from Benelux. This is kind of a flash sale as the BA promotion is running only till tomorrow. Roundtrip tickets from Amsterdam, Rotterdam, Brussels or Luxembourg are now available already for €343. Look for flights to San Francisco, Los Angeles, Las Vegas, Seattle or Denver. You have also some great opportunity to book open-jaw flights i.e. Benelux to Seattle and returning from California. Some of the flights require airport change in London on your inbound flight. This is great option to end you trip in the UK. It is up to you whichever solution you choose just make sure you book proper routing..
British Airways promotion is valid for flights departing to USA till end of October 2016 then from 1st of April till 16th of June 2017. Max stay 3 months. Discounted flights are valid for bookings made till 12th of October. Below you can refer to booking samples from each origin.
Booking samples
Belelux - US West Coast from €365 (directly with British Airways)
Amsterdam - US West Coast from €353 (flights without airport change)
Booking sample of an open jaw ticket: Benelux - Seattle & California - Benelux for €372
Travel dates. At this moment plenty of travel optíions are available in said period. If you still you can easily do so directly at the website of the airlines. Need a hotel in USA you may use Booking.com or consider following promo codes offered by Amoma, Hotelopia or Venere.
Booking sample of cheap BA flights from Benelux to US West Coast from €343 here. In this case you would depart from Brussels to San Francisco on 15th of May. Your return flight from California back to Europe would be on 28th of May 2017.