I have used Xchange Business -
http://www.xchangebusiness.co.uk - for the last 3 years.
I've sent money to NZ, Malaysia and Sri Lanka using them and they've always offered a pretty good rate. The spread is normally around 0.5% and there is no fixed fee on transactions over £1000.
For example:
Send £50,000 to New Zealand
Mid price of GBP NZD is $2.65
Xchange Business quote is $2.635
They make $0.015 commission per pound i.e. $750 or about £283
I have had quotes from banks and Xchange Business has always come out top. They reply to emails quickly and are also quick on the phone. You need to transfer the money to their account then they transfer it to the recipient account.
That said, I would still like to find a cheaper way of sending money if anyone knows of a company that offers a narrower spread.
To trade using Xchange Business, you first need to open an account and they need to see your passport and driving license (or a certified copy) so it's a bit of a hassle and takes a few days.