Porcelain Bonded to Precious Metal -- This is what the majority of crowns are made from. A precious metal base is made and porcelain is then applied in layers over it.
Porcelain -- These crowns are not as strong as bonded crowns but they can look very natural and are most often used for front teeth.
Porcelain and Composite -- Porcelain and composite resin materials can sometimes look the most natural. However, these crowns are not as strong as bonded metal crowns.
Glass -- These crowns look very natural and are used on both front and back teeth.
Precious Metal (Gold and Palladium) -- These crowns are very strong and hard-wearing, but are usually used at the back of the mouth, where they are not visible.
Source: [What are crowns made of?]
