I found SSHKeyChain to be one of the most useful utilities on MacOS X so far. The Website states Painless ssh key management for MacOS X and they don't exaggerate. I can just import new ssh keys (the ever growing list of SVN+SSH repositories...) and stop thinking about them. Apple's Keychain takes care of the passphrase management.

In addition, it comes with a small environment property list editor built-in: