I have just bought a Linksys WRT54G router, which has the ability to load custom firmware.
As there are lots of them around the web, Can anyone recommend a FOSS simple, powerful and stable firmware package that also supports port forwarding?
I'm running Tomato on my WRT54GL and I love it. It doesn't quite have all the features of DD-WRT but it been rock-solid and still has all the essential features, of course including port forwarding. It has a nice AJAX interface that can show you your bandwidth usage, has good QoS controls, lets you control tons of aspects of your wireless (many types of security, antenna power, etc). I'd definitely recommend it.
You can see your router in the list of compatible routers at:
You might want to check out X-wrt. It's Open-wrt with a graphical interface. The current release of Open-Wrt (and therefore X-wrt) is Kamikaze. Also woth considering is [freifunk]. It's Open-wrt White Russian with an interface and controls designed for a community mesh.