Random internet lag spikes.

For the past couple of months I have had lag spikes every couple of minutes on my computer. It not only affects WoWQ but other online games I play as well as vent, however it does not seem to affect the rest of the internet. It is driving me completely crazy and I have no idea how to fix it. I have tried plugging my computer directly into the router, removing all the unessential processes on my computer, removing firewalls, etc, and none clear up this problem. Is there anything I've missed? I am really desperate, this is making it really frustrating to play. My latency usually hangs at around 300-500 MS when it used to be less than 100.

There are three computers connected to the router and mine is the only one that has this problem.