SSHKeychain is an SSH key manager for Mac OS X:

It has long ceased to be necessary given that SSH is now properly integrated into the OS, but if you’re using a very old version of the OS, keep in mind it has a small bug (it gets confused with lots of forwarded ports), but you can edit the tunnel configurations directly in ~/Library/Preferences/SSHKeyChain.plist (just double click on it and add your tunnels under the Tunnels array).