To set up ssh to allow logins without having to type a password, first generate keys on the local machine:

ssh-keygen -t rsa

Copy (securely) the freshly generated public key (id_rsa.pub) to the remote machine.

Append the contents of id_rsa.pub to the ~/.ssh/authorized_keys file in the home directory on the remote machine.

Finally, if necessary:

chmod 600 ~/.ssh/authorized_keys

The above procedure will also stop SVN from constantly pestering for a password when checking out a repository. (For those of us unfortunate enough to still be using SVN.)