What is the most eco friendly way to clean your bike? I want to use a degreaser and other cleaning solutions that are biodegradable.
For most things, you can just wipe the bike down with a wet towel or sponge and it will be about as green as you can get and adequate (well, as green as you get would be to leave it dirty). Some dish soap and a hose (on shower setting, not jet or super soaker or whatever) if its really dirty. Don't use a pressure washer or something since you might get dirt into bearings or crevices.
If you want to use degreasers, citrus degreaser should be biodegradable depending on what brand you get for the chain. Park Tool among others make a convenient little thing you clamp onto the chain to clean it.
One link to look at is Park Tool's guide.
In addition to dish soap and citrus based degreasers there are also alcohol based one like the Finish Line's Speed Bike Degreaser. It does not require water and evaporates after application, thus minimizing your environmental impact. That said I usually the Finish Line product first to remove greasy messes and finish off with soap and water followed by just water.