Same here.
I normally use XE Trade to transfer my money. You get a quote to convert the money between currencies and then depending on how you transfer it, you may pay a charge for the transfer as well (last time I did it, an EFT transfer was free and a wire transfer was £12.50).
My bank gives a better exchange rate, but they charge £10 per transfer, so usually I find that XE Trade is similar or a little cheaper.
Just had a look on XE Trade for transferring dollars to pounds: if you transfer $1,000, you'll receive £618 in your UK bank - no fee with EFT transfer, or a $20 fee for a wire transfer.
Alternatively, you can also transfer your money via PayPal - open a US account with your US bank details and a UK account with your UK bank details and then transfer the money between them. Not sure of their exchange rate/fees though.