Daily Revolver

When it comes to firmware for your router most people only use that which comes with the hardware, and out of those people many never even bother to upgrade this firmare when there is almost always an online upgrade available with any newly purchased router. All that being said most of these people will get by fine with it and won’t ever find a need to upgrade or change and most certainly would never consider using something other than the  ‘out of the box’ experience.
The following two open-source router firmare applications are not for those people. Its for those who at the very least can manage to upgrade their existing manufacturers firmware with little or no problem. If you can do that (and its pretty damn simple in most cases) than you can use these open-source alternatives with no fear and get a lot more from your router.

Linksys, Belkin, Netgear, Buffalo, D-Link and many others are supported by both, so without further delay give consideration to either of these fine choices:

(.) Tomato is a small, lean and simple replacement firmware for Linksys’ WRT54G/GL/GS, Buffalo WHR-G54S/WHR-HP-G54 and other Broadcom-based routers. It features a new easy to use GUI, a new bandwidth usage monitor, more advanced QOS and access restrictions, enables new wireless features such as WDS and wireless client modes, raises the limits on maximum connections for P2P, allows you to run your custom scripts or telnet/ssh in and do all sorts of things like re-program the SES/AOSS button, adds wireless site survey to see your wifi neighbors, and more. [source]

(.) DD-WRT is free Linux-based firmware for several wireless routers, most notably the Linksys WRT54G (including the WRT54GL and WRT54GS). It is licensed under the GNU General Public License version 2.
Many of DD-WRT’s features are not included in typical router firmware. These features include support for the Kai network, daemon-based services, IPv6, Wireless Distribution System, RADIUS, advanced quality of service, radio output power control, overclocking capability, and software support for a Secure Digital Card hardware modification.
DD-WRT versions up to v22 were based on the Alchemy firmware from Sveasoft, which in turn is based on the original Linksys firmware. DD-WRT versions from v23 onwards, however, are almost completely rewritten. The Linux kernel part is based on the OpenWrt kernel, which started as a Linksys-based firmware but later changed to its own build framework. All of the firmwares are based on Linux, as are OpenWrt and Alchemy.
Through a partnership with Buffalo Technology, Buffalo will begin shipping routers pre-installed with a customized version of DD-WRT. [source] [description from wiki]