One of the best deals from California to Europe has been around for several weeks now with tickets from LAX to London Heathrow LHR at $555 round trip for nonstop flights with United, Virgin Atlantic/Delta and American/British Airways.
Departure dates are early January to May 11 with most dates available.
Prices drop to $530s for one-stop flights with Delta/Virgin Atlantic via Las Vegas or Aer Lingus/AA/BA via Dublin. Also, these flights tend to arrive and depart at London Gatwick LGW.
Personally, I would go for a nonstop directly from LAX to London and avoid the potential for a missed connection.
Delta Airlines ticket for Virgin Atlantic operated flights Los Angeles LAX – London Heathrow LHR nonstop
United Airlines Los Angeles LAX – London Heathrow LHR nonstop
American Airlines Los Angeles LAX – London Heathrow LHR nonstop