I know people keep knocking Tomato and recommend DD-WRT with SPI Firewall off, but I've had nothing but solid service for a month+ running Tomato with a few "tweaks". See my sig for details. There isn't an option to turn the firewall off in Tomato. At least for me, it just works.

I've had DD-WRT, and have had great luck with that as well, but I'm not comfortable turning off the only defence between the internet and my home systems (unless you cascade routers and hook all the systems to the internal router, which I did with DD-WRT, and also still do with Tomato just because I'm lazy and don't want to rewire things).