While death knights have only been around for a couple of years and retribution paladins are tasked with rediscovering themselves every few months, rogues have remained consistent throughout WoW's entire lifetime. We've obviously received tweaks and changes along the way, but the rogue of today looks an awful lot like the rogue of the past. Over the years, the rogue class has been dissected from every angle, and our studious brothers and sisters of the shadow have discovered its secrets.
There are three main areas of rogue research: mathing out how the class works (and yes, mathing is a verb), picking the right gear, and figuring out the best specific strategies. The best and brightest rogues are constantly monitoring our DPS models to ensure their continual accuracy, compiling lists of the best gear and how to get it, and detailing their guides for dealing with players and raid bosses alike. I can say with a tremendous amount of bias that Encrypted Text is the best source for rogue info, but of course there are other sites that are useful as well.