VPN Router... Note: VPN Router has been discontinued as of 2009-03-24, click on "More Information" for details.
VPN Router lets you define a list of remote IP addresses to which all traffic should be routed through the VPN tunnel. Technically speaking: It adds static routes to your routing table as soon as you establish a VPN connection.
Here's an example: Your local network is 192.168.111.X and wires your beloved Mac (192.168.111.10) and a printer (192.168.111.20). You'd like to establish a VPN tunnel to a remote network 192.168.222.X. Once the VPN is established, all traffic for 192.168.222.X is routed through the secure VPN tunnel whereas all other traffic is routed as usual. Unfortunately, there is a remote server 192.168.223.223 you should work on, but you don't reach unless you configure VPN to "send all traffic over VPN connection". Then again, if you do that, you won't be able to print on your local printer anymore.
VPN Router is donationware which means that you can download a fully functional copy for free, however, you are kindly asked to donate US$ 5 or more per copy.