Just to give you an example:
If you were to change £500 today at the Post Office you would get:
543.40 Euros or $703.10
Change the same amount through this site you will get:
561.45 Euros or $720.00
As we all know our currency is in a bit of a state right now, I for one am a bit nervous about the exchange rate at the moment. The government are talking about Quantitative Easing (printing more money) which if happens will weaken sterling even more, making spending money for the summer holidays even more expensive.
Right now the exchange rate is actually looking a bit better than it has the last few weeks currently: 1.14 euros to the pound and just under 1.45 dollars to the pound.
On the Money Saving Expert website I found the site above a lot of well respected high post members recommended it on the forum as did the main site. The way it which it works is you change your currency now (minimum £300) and they send you your foreign currency a few weeks later, generally the longer you are prepared to wait the more money you will get. They put your money in a high interest savings account (probably in stronger currencies with higher interest rates) then at the right time they buy the currency you want and send it to you by special delivery. As I have said several high post members have tried and recommend this service, as have other posters so I would defiantly say its save.
Link to Money Saving Expert Currency finder: http://travelmoney.moneysavingexpert.com