Argiope bruennichi - Wasp Spider. Spotted in France on holiday. Scared the living daylights out of my kids and to be honest I wasn't too comfortable lying in the grass next to it to get this shot. (I have no Macro lens)
Apparently its harmless to humans as it turns out, but it was lethal to grasshoppers and flies wrapping and biting them repeatedly in seconds. As an extra bit of information the distinctive zig zag in the web is thought to be for attracting insects and/or to make it visible to birds so they don't destroy the web.