For me, for one I have been to, it's Autzen Stadium right here in Eugene, Oregon. Widely regarded as one of the toughest places to play in all of college football, the atmosphere is absolutely cracking. The design of the stadium actually aids in trapping the noise inside and really making it hard for other teams to play. Unlike most other stadiums, it's actually built into the ground a bit - and then is built in a bowl shape, rather than the more traditional rectangle shape of most. Having been there myself, I can testify to how f**king loud it is. It's brilliant! And I was only in the cheap standing room spots up the top, apparently in the lower stands and field level it is MUCH much louder.
Autzen is known for its crowd noise. The fans are very close to the field compared to other stadiums and the field is sunken, which contributes to the loudness of the stadium despite having a smaller capacity than several other stadiums.[17]. On October 27, 2007, during a 24–17 defeat of the USC Trojans, a then-record crowd of 59,277 fans was recorded at 127.2 decibels. A similarly-loud 31–27 upset of third-ranked Michigan in 2003 prompted a Michigan Daily columnist to write[18]
“Autzen's 59,000 strong make the Big House collectively sound like a pathetic whimper. It’s louder than any place I’ve ever been, and that includes The Swamp at Florida, The Shoe in Columbus, and Death Valley at Louisiana State. Autzen Stadium is where great teams go to die.”
Michigan coach Lloyd Carr later said that Autzen Stadium was the loudest stadium he'd ever been in.[19]
In 2006, a Sporting News columnist named Autzen the most intimidating college football stadium in the nation.[20]
Lee Corso of ESPN College Gameday frequently says that; "Per person Autzen Stadium is the loudest stadium that I have ever been in my entire life!"[21]
Jahvid Best, a starting running back for the California Golden Bears said of his game in 2007 at Autzen Stadium, "The biggest thing I remember about that game is the crowd. The crowd noise is crazy up there. Honestly, any other away game I don't really even hear the crowd. Oregon was the only place where it really got on my nerves."[22]
As a head coach for the California Golden Bears, Jeff Tedford said, "Their fans are so educated that they're really prepared as far as when to make noise and when not to make noise. You can quiet some crowds down if you score early and things like that. Not in Autzen. They're going to keep roaring the whole game, that's just the way they are."[23]
http://en.wikipedia.org/wiki/Autzen_Stadium