Personally I've tried Sonex Wiltec foam and some generic pax.mate akasa type stuff; the Akasa was useless, and the willtec is OK for high/mid frequency whine, but too light to do much else. It's reasonably cheap though, so for the price I'd say it's pretty good. I've also helped a friend put the acoustipack deluxe stuff in his case (and will soon be putting it in mine, after hearing the before and after on his!), and that stuff seems to be the best, but it's NOT cheap. The acoustipack stuff is very heavy and really deadens vibration and whine. It's something like 60 bucks for the standard pack and 80 for the deluxe set. So I guess it depends on what you consider Worth The Cost. The Acoustipack definitely works, but is expensive, while a lot of other stuff is cheap but doesn't do squat.
SPCR's got a review on the subject, mainly the Acoustipack, as they dismiss the other contenders as worthless:
http://www.silentpcreview.com/article71-page1.html