Casascius 1000 BTC gold coin
The Casascius 1000 BTC gold coin is the highest denomination coin ever produced by Casascius. It is also the most valuable physical bitcoin ever produced, with one selling for $1 million in 2013. The token is made of an ounce of fine gold, which at the time of production was about one third the value of the 1000 BTC. The coin could be ordered directly from Casascius for approximately $5,500.
As the value of bitcoin rose through the April and November 2013 bubbles, the value of this unopened token quickly appreciated, going from $10,000 to $1 million. As of March 2015, a reasonable price is $300,000.
With the rise in value of Bitcoin in late 2017, as of January 2018, 1000 BTC is worth ~$15,000,000.00 USD, making the 1000 BTC Casascius coin likely the most valuable coin in the world.