I second the idea of the breathable waders. Even in the cold. I received a pair of breathable waders & felt sole boots last year for Christmas and I will probably never go back to neoprene waders. When its really cold out, I start with a base layer of expedition weight MTS thermals from REI on the top and bottom, then over that goes my Polartec 300 weight fleece pants & top. Never been cold with that combination.

One added note, cotton is about the worst thing you can wear in cold wet conditions, polypro or Polartec fleece all the way. It will keep you warm even when wet & it dries very fast. Cotton will stay wet all day and suck every ounce of heat from your body. (In My Humble Opinion) 10 years of guiding whitewater trips getting hammered with ice cold waves from spring runoff in the rivers have taught me some valuable lessons about keeping warm.

Rafterman