Is this a return trip, and if so, for how long?
 
With flyzoom.ca you can get LGW-JFK roundtrip for 302 pounds total, for July 3-17, or many other dates.
 
If you want one-way, you can also get that.

I don’t know if you’ll do better than what Traveler found. That’s about $735 with Eurostar (does that stop at Heathrow?).

In addition to tips and links in our new user thread (top of this forum), you should also try Belgian airfare consolidator Travelprice, as well as Kelkoo Belgium’s Airfare Shopper.

ITA turned USAir at $875 from BRU-NYC (via PHL) with some availability outbound first half of July, midweek. Orbitz flex turned up $831 on Swiss via GVA each way (5th\18th). That’s only $100 more than Eurostar+Zoom from London. If these interest you, best to track it down and book direct from the airlines’ websites: www.swiss.com or www.usair.com — but see if Travelprice or Kelkoo turn up something better.

Thanks for your replies!

It’ll be round-trip. I’ve checked out those sites you mentioned, and flyzoom and travelprice are definitely very interesting!