Don't forget about Ultra High Molecular Weight Polyethylene (UHMWPE). This fantastic stuff is used in surgical implants, such as replacement knees and hips. It is tough enough to replace sections of bone, but has enough cushion and low enough friction to also replace the cartilage in a joint. It has incredible wear characteristics (think of how much abuse your knee takes each day) and is relatively easy to machine. The only downside is that sterilization generally leads to the formation of free radicals, which adversely affects performance.