Snipit to add to bash_profile that will find an existing ssh-agent or start a new one. Also complains if it finds more than one for a user.

ssh-agent.sh

# Attach to a running ssh-agent or start a new one
if [ `find /tmp -maxdepth 1 -name "ssh-*" -user ${USER} | wc -l` == 1 ] ; then
  echo "Found ssh-agent, attaching.."
  SSHDIR=`find /tmp -maxdepth 1 -name "ssh-*" -user ${USER}`
  SSH_AUTH_SOCK=`ls ${SSHDIR}/agent*` ; export SSH_AUTH_SOCK
  SSH_AGENT_PID=`echo ${SSH_AUTH_SOCK} | awk -F"." '{print $2+1}'` ; export SSH_AGENT_PID
  echo "Agent pid ${SSH_AGENT_PID}"
elif [ `find /tmp -maxdepth 1 -name "ssh-*" -user ${USER} | wc -l` == 0 ] ; then
  echo "no ssh-agent found, starting.."
  eval `ssh-agent -t 86400`
else
   echo "####################################"
   echo "# ssh-sgent in a suspicious state! #"
   echo "####################################"
fi