Being a founder shareholder for Out of this World, I was interested to discover The Peoples' Supermarket, who have just launched into a Meanwhile (i.e. temporary) space in London. The interesting thing about this isn't that its a co-operative supermarket - that's been done before. It's that you have to commit to work in the shop for a couple of hours a week to buy things from it. It's non-profit and worker owned, making it very cost-effective...
http://www.peoplessupermarket.org/
http://www.facebook.com/group.php?gid=107558762604771&ref=ts#!/group.php?gid=107558762604771
Simon