I attempted to transfer my Etererum holdings from Bitcoin to an address and entered a wrong digit in the address. Coinbase shows transaction complete. How can I recover?
Simple! You just brute-force as many random private keys as you can until you find the one that corresponds to the address you accidentally sent your Ether to. Only downside, this will probably take you longer than the remaining lifetime of the universe.
Alternatively, lobby the Ethereum community to create a hard fork of the blockchain just for you, in which that transaction didn't take place. I wouldn't hold your breath on this option either.
Third option, ask coinbase nicely and see if they will issue a refund. This is probably the least likely option to succeed of the three :)