Have you ever wanted to bundle/bond/combine devices together to increase your available bandwidth or load balance your routing? pfSense has been able to do this since its alpha version. pfSense is in 1.0 Beta 4 now, with RC to be released very soon. pfSense also supports QoS, so you can run BitTorrent & VoIP at the same time. Kick that iptables script or vendor X's firewall/router solution aside & move to pfSense!
dual wan instructions
other pfSense tutorials (including VMWare installation)
pfSense mailing lists and ##pfsense on freenode IRC
why pfSense sucks (for the cynics)
pfSense is the most advanced Open Source Firewall project as of this writing. Take a look at the pfSense feature set.