Is there a GUI front-end to Apache for Mac OS X (Lion)?

There's no built-in GUI, but there are third party ones. One that I know of for managing virtual hosts is called VirtualHostX: http://clickontyler.com/virtualhostx/

No, there is no GUI for the built-in apache. This is how I just set mine up so I can add my own VirtualHosts more easily:

sudo -s
mkdir /etc/apache2/vhosts
chgrp admin /etc/apache2/vhosts
chmod g+w /etc/apache2/vhosts
cat << EOF >> /etc/apache2/extra/httpd-vhosts.conf
#
# Load user-defined vhosts
#
Include /private/etc/apache2/vhosts/*.conf
EOF

This adds a vhosts directory under /etc/apache2/vhosts. You just need to turn on vhosts in the master /etc/apache2/httpd.conf file, and then it will look for all .conf files in that vhosts directory. I made it so as an admin user I have privileges to save in there.

It's a little tidier than trying to put everything in one file like the example vhosts in the config file.