Additions to the library for today, October 27, include Rage, Killer Is Dead, and Shred Nebula. Microsoft's Larry "Major Nelson" Hryb announced these through his Twitter account today.
If you already own any of those games on Xbox 360, they should show up automatically in your Xbox One game library. One thing to note that is Rage requires the Xbox 360 game disc; it's not available digitally. You can buy Killer Is Dead and Shred Nebula through the Xbox Store or via the links below.
Last week, Microsoft added The Orange Box (containing Half Life 2: Episode 2, Team Fortress 2, and Portal), Galaga Legions, and Joe Danger 2: The Movie to the backwards compatibility catalog.
The Xbox One's backwards compatibility feature launched in November 2015 with the New Xbox One Experience update. Microsoft has added new titles on a regular basis since then--you can see all 250-plus games in the catalog here.
Recently, Xbox boss Phil Spencer was asked if Call of Duty: Black Ops II--the most-requested title on the Xbox Feedback site--would be added to the program. He did not confirm anything but said conversations are ongoing about adding more third-party games to the catalog.