I was always a two pair sort of bloke until I discovered Harkila. They make astoundingly good socks. I was stood in the snow yesterday for hours with one pair of Harkila socks under a pair of Nora wellies (you know, dairy wellies, not thick, not lined) and my feet remained toasty.
As someone also pointed out, Muck/Grub boots are damn good too...but beware of the stench after prolonged wear!!