I am using a Linksys WRT54GL with a custom Tomato 1.28 firmware. It works fine, but for whatever reason, even though I forward ports for various things (to the proper IP of 192.168.1.100), various port testing sites claim the ports aren't open and I can't host things in games like Killing Floor.
I may be missing something obvious, but I've forwarded ports in the past on a different (though still Linksys) router and had no trouble getting things to work.