BA and Virgin, sometimes Continental but they are code share partners with Virgin, so you usually find yourself on a Virgin flight if it's Continental direct. This seems to be out of LGW rather than LHR in my experience. Don't know about other airports.
Most US carriers do indeed go through their main US hub.
If you go to somewhere like Opodo or Expedia and put in your dates and choose 'direct flights only' you'll soon discover your options. If your dates a later than 11 months or so from now just make up some dates to see what's available.