If its super muddy I agree with the garden hose, just remember to use low pressure near any bearings. I've used Pledge extensively for frame wipe downs and helps keep dirt/mud from sticking for a while. These days I've using a spray wash from the automotive section on my personal bikes. Works great, shines great, leaves a wax to provide protection. Current favorite is Meguiars Ultimate Waterless Wash and Wax. ONR makes a great product as well.
Drivetrain is simple. Simple Green, that is. Couple years back I picked up one of those on-bike chain cleaners and its simply awesome. Always used to pop the quick link and clean them off the bike but this is SO much easier and just about as effective.
Edit: As alluded to above, riding a trail during heavy mud does damage the trail, sometimes severely. Please try to avoid those conditions unless your local trail maintenance organization is specifically OK with it.