linkback: http://www.karan.org/blog/index.php/2009/08/25/multiple-ssh-private-keys

ssh-keygen -t rsa -f ~/.ssh/id_rsa.acquia -C "Key for my Acquia accounts"
touch ~/.ssh/config
chmod 600 ~/.ssh/config

~/.ssh/config looks like this :

Host *acquia*
  IdentityFile ~/.ssh/id_dsa.home
  User jbarnett

Host *babson*
  IdentityFile ~/.ssh/id_rsa.work
  User jbarnett
  Port 44787