Where are my private/public SSH keys on UNIX?

I'm starting to understand how RSA and public/private key systems work, and I was wondering where my private and public SSH key are stored. When I go to my home directory, and I browse my .ssh directory (cd .ssh), I only see the "known_hosts" file, which I guess contains the public keys of different remote SSH servers I know.

Where can I find these keys? I don't even remember creating them by the way, but since I've already established ssh connections before, they must be somewhere.

I'm using OpenSSH_5.2p1 with MAC OS 10.6.

Thanks!