I surprised that nobody mentioned this. "Var #232 Chainring bolt tool.This is the ultimate weapon for stuck chainring bolts. The tool grabs the two notches in the nut, with perfect alignment, while also the T handle engages the Allen bolt. When you need this tool, nothing else will do. $39.95"
It's on the Harris Cyclery web site,
http://sheldonbrown.com/
Roy "the right tool for the job" Drinkwater Lititz, PA
VGhpcyBpcyB0aGUgdWx0aW1hdGUgd2VhcG9uIGZvciBzdHVjayBjaGFpbnJpbmcgYm9sdHMu IFRoZSB0b29sIGdyYWJzIHRoZSB0d28gbm90Y2hlcyBpbiB0aGUgbnV0LCB3aXRoIHBlcmZl Y3QgYWxpZ25tZW50LCB3aGlsZSBhbHNvIHRoZSBUIGhhbmRsZSBlbmdhZ2VzIHRoZSBBbGxl biBib2x0LiBXaGVuIHlvdSBuZWVkIHRoaXMgdG9vbCwgbm90aGluZyBlbHNlIHdpbGwgZG8u