+1 and cheap from Euro Car Parts (and similar outlets)Aerosol brake cleaner.
It washes everything off, not just grease but any grit and evaporates away to clean lovely dryness.
To be guilt free and green you'd have to be using one of the 'green' lubricants too. Otherwise an enviro friendly cleaner seems a bit pointless if you're just washing the greasy gunk off anyway, unless you clean the bike in the bath and catch it. Don't think theres much to worry about there though compared with motorised vehicles.Jizer. About £20 for 5 litres or something. It doesn't smell of citrus fruits, it isn't organic or approved by The Soil Associaton but.......it doesn't come with a poncy bike shop price tag, and it works. Big time.