Tunnelblick is a very nice GUI for OpenVPN. A tunnel icon is added to the menu bar. You can click on the icon to connect/disconnect to your VPN.
The "stable" version (2.0.1) allows for connnecting to a single VPN. You create a ~/Library/openvpn directory and save your configuration file as openvpn.conf.
The 3.0 Release Candidate (I just now noticed that RC2 is out) allows for the ability to connect to multiple VPNs depending on the name of your configuration file. Save your configuration file as Server1.conf, Server2.conf (where "Server1" is an arbitrary string).
I can't see using OpenVPN on a Mac without it.