While setting up an automated rsync over SSH, I learned about the useful keychain utility which makes using ssh-agent easier for passwordless authentication. Although the links to the project's source code were dead, "yum install keychain" conveniently installed it in Centos.

Keychain has a weird bug, howver, which prevented it from working for my use case. If you have problems with keychain, try putting this code in your .bashrc (here's the source of this tip):

function kc() {
#Keychain invocation
keychain ~/.ssh/id_rsa
if [ -e ~/.ssh-agent-`hostname` ] ; then
source ~/.ssh-agent-`hostname`
elif [ -e ~/.keychain/`hostname`-sh ] ; then
source ~/.keychain/`hostname`-sh
fi
}

Once this code is in your .bashrc you'll be able to enter "kc" to work around keychain's issue.