Open Source Gateway Server
One of the first "projects" I embarked on when I first started using Linux was a gateway/router box. I had a switch (instead of a router) and rather than just go buy a router, I made one. This allowed me to ssh into my house from away, and then on toward any of the running boxes on the inside of the firewall.
The box was an old Dell, with a Pentium II. I used CentOS 4, and it ran for a good five years before the motherboard finally crapped out. Rather than go set up another box, I just robbed one of the nics and stuck it in the computer that's always running here. I made that Ubuntu (Lucid) box into an open source gateway / router fairly easily. I think I followed along with this page about open source gateway / router setup. This setup only took a few minutes that I remember, rather than the couple of hours for the first one I made way back when…
Now, rather than log into a gateway / router / firewall box, then hop through to the desktop box, I'm right there immediately. Unfortunately, so is anyone else. If you're going with this setup, you'll want something like denyhosts setup that will block folks after a predetermined number of failed login attempts.
My current setup is DSL Modem –> Ubuntu Lucid desktop –> Wireless Router (set up as an access point) –> rest of house (via switch) Using Ubuntu as an open source gateway and router means that I can configure things much more than by using most off the shelf hardware. I don't require much, so I'm not using it to anywhere near its full potential, but the options are there if I want to employ them.