http://www.travelex.co.uk/uk/
are also looking good at the moment, just got a quote from them for £510 quid converting to E603 either as cash or on one of their currency cards. Their delivery charges are cheap too, £1.95 for orders over £500 . Post Office are also apparently offering ther same rate.
Now is def the time to buy euros, even for those going in the Summer (so the advice goes!)
for those who are out all day so can't sign for deliveries of travel currency (like me) - I found the Post Office very competitive. order online, and collect and pay at any post office you specify.