Another bad thing about detergents is that any left on will act as a magnet for road grime (that's exactly what detergent in your car's oil is supposed to do, but you don't want that happening on your chain).

Hmmm, no mention yet of Citra-Solv? It's an awesome general household solvent. It's biodegradeable. My wife uses it extensively in her eco-cleaning business, so we buy it by the gallon; much cheaper than the little bottles. It can vary wildly in price, based on whether it's sold for specialty or general purpose use (it's the same stuff, tho'). Be careful, though. It may be gentle environmentally, but it's potent stuff. I dripped some on a tile floor in our previous apartment, and it slightly dissolved the surface of the tile!