Linksys makes a line of cheap, ubiquitous router/firewall boxes (models BEFSR41 and up, including the WRT54G) well-suited for use on a home DSL connection and popular among Linux hackers. This HOWTO gives hints and tips for managing Linksys routers from a Linux system, including the firmware upgrade procedure.
This HOWTO is no longer actively maintained, because as of 12 Oct 2006 the author is no longer a Linksys user. Time and technology nmarch on, and I now have a much fancier router in my basement that came with my optical-fiber service. If you are qualified and interested in taking it over, contact me.