I'm going with giffgaff for a 2 weeks trip next week. I had a sim sent over by following the links in this thread at the giffgaff community - it arrived within a few days from a giff-gaffer: http://community.giffgaff.com/t5/Con...d/td-p/8052456

All you need when you get there is to buy a 10UKP giffgaff/o2 card and you're all set. Depending on who sends your sim they also offer to send you a voucher so you don't need to find a shop when you get there.