Most people who use vyatta say its better than flashing routers with ddwrt/openwrt/tomato-usb etc.
Vyatta is a good project, that is a dedicated network OS based on -- linux. It provides security and all routing mechanisms to build a low-cost, low-power consumption custom made router out of a computer or other small form factors.
Open-source and free to download:
http://www.vyatta.org/