Linkin Park will release the 20th anniversary edition of Hybrid Theory on October 9. The anniversary edition features some live tracks, demos, and b-sides depending on which version you get. You can hear an early version of the band's massive hit "In The End" right now, which is pretty radically different from the version you all know. Instrumentally not so much, but all the rapped verses are entirely different.
Hybrid Theory recently went 12x Platinum in the United States, meaning the album has sold over 12 million copies. Pre-order the box set here.