You can use this stuff to secure your home network like Fort Knox. It won't keep Big Brother out (because he will kick in your front door at 3AM if he REALLY wants something), but it will certainly make Little Brother's life difficult.
Check out the OpenWRT project. OpenWRT is a Linux distribution for embedded devices, and it brings a lot of exciting possibilities to your humble wireless router. Although still in its release candidate stage (currently at RC6), OpenWRT is very usable and feature-rich right out of the box. Be warned, you could void your manufacturer warranty by installing OpenWRT on your wireless routers.
So what can you do with an embedded Linux device running on limited RAM and very small storage? As it turns out, quite a lot actually. You can install asterisk, and have your personal, customizable PBX (private branch exchange). If you already have a SIP phone or some kind of VoIP phone interface (such as the Cisco ATA 186 adapter), you can have your very own VoIP system at home, all running out of your low power-consumption embedded hardware.
Put your router/firewall on steroids by installing packages like nmap (network security scanner), snort (intrusion detection), and tcpdump (packet sniffer). Together with iptables (which comes with the Linux kernel), you can turn your OpenWRT box into a powerful security tool. Install openvpn, and you have a very affordable VPN device. And if it strikes your fancy, you can install quagga and turn your dusty little Linksys into an OSPF and BGP-capable router.
Want to provide your own wireless hotspot? No problem. Install chillispot, and you are ready to go. You can even install FreeRADIUS on the OpenWRT for the authentication back-end, and WPA (wifi protected access) for the added security.
You can turn it into an all purpose office server by installing DHCP, cups (print server), lighthttpd (web server), NTP (time server) and OpenSSH or dropbear (secure remote administration). If your router has a USB port, you can also turn it into a file server by hooking it up with a USB hard drive and installing NFS.
And don’t forget that this is a wireless router. It has a wireless card, so take advantage of it! Install kismet on it, and you have a wireless sniffer. This can prove to be invaluable if you ever need to analyze the airwaves at a remote location, but don’t want to leave your expensive laptop on-site. Drop in place a $50 OpenWRT box loaded with kismet instead.