It's also been proven that it doesn't matter several times also. I have seen some pretty heated battles on the Audio Video forums, about HDMI, optical, and speaker wire prices and quality. I always just buy the cheapest I can find. Sometimes it has been 60$ 3 foot HDMI cables and other times it has been 5$ 10 foot cables online. I honestly don't even pay attention to which ones I'm using. I just grab the one that is the best length, and go with it. I have never been able to tell a difference with sound, or video. The only problem I have had with a few really cheap cables is the build quality. A few have came apart on the ends pretty easy.
I would also like to second the monoprice link. Quality made cables and a great price.