(ok this won't help RIGHT this second but...)
If you do odds and sods on the car, get a set of these:
http://www.ebay.co.uk/itm/7-Grip-Tite-Style-Mac-Allister-Sockets-3-8-Set-for-Rusted-or-Rounded-Bolts-Nuts-/121662898615?pt=LH_DefaultDomain_3&hash=item1c53ac81b7
buy me a beer after they've worked their magic