Use in Video Games

Nine Inch Nails and Trent Reznor's music has been used in video games, ranging from the first person shooter Quake to music games Guitar Hero and Rock Band.

Quake

The Quake Soundtrack was wholly created by Trent Reznor for use as background and incidental music during gameplay. The 10 tracks created for this release have never been released elsewhere, and therefore an original copy of the soundtrack is prized by many.

Doom 3

Reznor was originally approached to create sound effects and music for Doom 3, and his pieces were used in the original alpha release. However, the final game didn't contain any music or sounds by Reznor.

Note that id Software were such fans of Nine Inch Nails that the Ultimate Doom game featured the NIN logo hidden on the level map "E4M1: Hell Beneath"

Tony Hawk's Project 8

The soundtrack for Tony Hawk's Project 8 features "Getting Smaller"

Tap Tap Revenge

The iPhone exclusive game "Tap Tap Revenge" premiered its first ever special edition version of the game with Tap Tap Revenge: Nine Inch Nails, featuring 13 tracks from Ghosts I-IV and The Slip, hand-picked by Reznor. This is also the first game that was co-designed by Reznor, along with long-time art director Rob Sheridan, highlighting a desire that both have pledged for making a full-blown video game.
The tracks used are:

Rock Band

Rock Band features 7 fully playable songs from the NIN catalogue,

"The Hand That Feeds" - From the original game

From the separately purchasable "Nine Inch Nails Pack 1", released February 26, 2008:

From the separately purchasable "Nine Inch Nails Pack 2", released July 22, 2008:

Guitar Hero: Warriors of Rock

Guitar Hero: Warriors of Rock featured "Wish", fully playable.

Need for Speed: Undercover

The soundtrack for Need for Speed: Undercover features the song "The Mark Has Been Made"

Midnight Club: Los Angeles

The soundtrack for Midnight Club: Los Angeles features "1,000,000" and "Discipline" (listed under "Hard Rock")