The big guy gets more competition every year now. This time it's Mapusaurus roseae, a close relative of Gigantotosaurus, which knocked T. rex of its pedestal back in 1995.
This now puts T. rex fairly far down the list of "biggest meat eaters of all time." The current champion, as of a few weeks ago, is Spinosaurus, an early Cretaceous critter from North Africa, featured in Jurassic Park III. Then we've got Mapusaurus and Giganotosaurus, both of which hailed from Argentina in the late Cretaceous. The two giant meat eaters probably used pack tactics to hunt down the mighty sauropods that roamed the plains of Patagonia. Which of the two was bigger? Not sure, but they're both bigger than T. rex.
And both of Giganotosaurus and Mapusaurus were members of the Carcharodontosaur (shark toothed) family of meat eaters. Their African relative, Carcharodontosaurus, may have been as big, if not bigger, than T. rex as well.
So the best case scenario right now is that T. rex is the fourth or fifth biggest meat eating dino ever discovered. Still, he had a 90-year reign at the top. From discovery in 1905 to being dethroned in 1995 is a pretty good run.