I too usually use ATM's when travelling overseas, but in February there were many currency exchange places in London offering some incredible rates for US 100 dollar bills. Had to be Hundred dollar bills, not 2 fifties or 5 twenties. I didn't have any with me, but next time I will certainly bring some. I don't want to know why they needed 100 bills so badly, but the exchange was way above the regular rate and what the ATM was giving.

By the way, I don't pay a fee for ATM transactions out of the US either, which in a way pisses me off since I have to down the street (should I choose to use that ATM). Makes no sense to me.