David Eck has a nice book and web site for his easy-going book, The Most Complex Machine. He has a Turing Machine simulator.
Simulators:
I had intended to also talk about "blocked cellular automata" (BCA), aka partitioning cellular automata aka lattice-gas automata aka CA with the Margolus neighborhood. This is a very elegant alternative definition for CA rules; several homework problems refer to it. It's usually defined for 2D CA, but the 1D simplification is obvious, and also interesting. The "billiard ball" cellular automata is the classical 2D example, and a good way to explain this type of rule. Some "Billiard Ball" simulators: