I'm looking for a recommendation for a GUI SCP client that supports private keys.
All of the ones I find don't support private keys. Thanks
Transmit by Panic - http://panic.com/transmit/
Configure as an SFTP server, click the Key icon.
I'm not sure of the specific implementation (SFTP vs SCP), but testing onto another standard OS X host with SSH keys setup works fine. The other box isn't running a special SFTP setup - appears to work fine.
Transmit is a great OS X app for any sort of file transfer.