Hi all. I highly recommend using
www.kayak.com for flight searching (they have a uk counterpart as well). They scour all the sites and get you a concise search response in moments. I definitely recommend this for you, Little Miss Sarcasm if you haven't bought your tickets yet already.
We had an opposite one way vs return experience. We purchased our LAX - LHR tickets for around $600 each (including all taxes) on Air New Zealand because Virgin, which we usually religiously fly, and all the other airlines, were charging well over *$1000* each way, and their return tickets were even more! Since we don't have a set return date, the ANZ tickets rocked our world.
I think in the end it depends on the time of year you are going. Nursefoxfire, you are going right in the middle of peak travel time. You may find that just a month later, fares go down by almost $300! Not only do airlines hate one way travellers, they hate one way travellers who travel mid summer!