anti-rust surface treatments

• powder coating
  used on bicycles
• tin plating
• zinc plating
• galvanization
• black oxide [1] [2] [2]
• phosphate coating
• blacksmith treatments of oil/beeswax [1] [2] [3]
• bluing
• more

wear-resistant coatings

• hard chrome — long the king of wear-resistant coatings, its cost has driven people to alternatives
  • thermal spraying, particularly HVOF
• Electroplating — theoretically there's no limit to the thickness
  • nickel plating — sources differ on the maximum thickness that's practical, but somewhere between 0.1mm and 0.8mm

aesthetically-pleasing coats (metalic)

• nickel plating
• chrome plating

aesthetically-pleasing coats (non-metalic)

• powder coat

general high-level reading material

• wow, really great info