Amazon offers a ton of games with credit when you pre-order. So, if you preorder a game via Amazon that has a gaming credit bonus you'll get that shortly after they ship it out to you. If you use that credit to buy another game with and roll it over for all of eternity. This helps support the site by the way. Plus, you can get release date delivery for only 99 cents more, so it'll be just like picking it up in the store only (hopefully) cheaper.
Here's there list, it changes frequently depending on what other retailers do:
Star Wars: The Old Republic Early access to the game
Gears of War 3 Standard Edition $20 Game Credit Plus Exclusive Savage Kantus Multiplayer Code, Limited Edition and Epic Edition only gets Savage Kantus code
Gears of War 3 Limited Edition Console w/ 320 GB HD with Savage Kantus code
Madden NFL 12 $20 Credit and All Rookies and All Sophomores Team (PS3 and 360 versions only, Standard or Hall of Fame Editions)
Elder Scrolls V: Skyrim Premium Physical Map
Call of Duty: Modern Warfare 3 PC, PS3, Xbox 360 Get Wallpaper and 360 version gets Special Forces Avatar as well.
Halo: Combat Evolved Anniversary Master Chief Avatar Armor and the Grunt Funeral Skull (once activated, every grunt's methane tank will explode like a plasma grenade when killed)
FIFA Soccer 12 $20 credit and MLS Fathead Teammate 12"x12" code for PS3 and 360 versions. $10 credit for Wii + MLS Fathead code. PSP, 3DS, PS2 only MLS Fathead code.
Rage $10 gaming credit and upgrade to Anarchy Edition
NHL 12 $10 credit and 3 digital issues of Hockey News
Batman: Arkham City $10 credit for PS3 and 360 versions, Collectors Edition ($99) gets Batman: Arkham City Comic
Forza Motorsport 4 Limited Edition Subaru Impreza WRX STI code
Deus Ex: Human Revolution Standard or Augmented Editions - Code to unlock a Tactical Enhancement Pack
Dead Island Digital Art Book
Shin Megami Tensei: Persona 2 Innocent Sin Bonus Mini-Soundtrack
Saints Row: The Third (Standard or Platinum Edition) Code for Professor Genki Pack
No More Heroes: Heroes' Paradise Code for Cross Saver weapon and Moto Magazine 2 bike
Lord of the Rings: War in the North $20 credit PS3 and Xbox 360 only, all versions also get Orc Champion Sword code
The King of Fighters XIII 4-CD soundtrack compilation
Ultimate Marvel vs Capcom 3 New Age of Heroes Costume Pack code
Warhammer 40,000: Space Marine and gain access to an in-game Golden Relic Chainsword.
Mass Effect 3 $10 credit
NBA 2K12 $10 credit Wii, Xbox 360, PS3 versions only
El Shaddai: Ascension of the Metatron $10 credit
Twisted Metal Receive a DLC code for Axel
Need for Speed: The Run - Limited Edition (PS3, Xbox 360, PC) Underground Challenge Series which gives you access to two bonus cars and three events inspired by Need for Speed: Underground as well as Limited Edition features including the Lamborghini Aventador, Chevrolet Camaro ZL1, and the all-new Porsche 911 Carrera S along with five exclusive events.
WWE '12 Playable 'The Rock' character code
Tropico 4 $10 credit
Spider-Man: The Edge of Time PS3/360 Get early unlock of Future Foundation costume
X-Men: Destiny PS3/360 versions only - Early unlock of Emma Frost suits
Driver: San Francisco PS3/360 only- 1964 Aston Martin DB5 multiplayer car code
Rise of Nightmares Jester Avatar Pet
Stronghold 3 $10 credit
Spec Ops: The Line $10 credit
Final Fantasy XIV PS3 only, $10 credit
Sharkoon X-Tatic SR Gaming Headset $10 credit
PlayStation 3D Display Get bonus Resistance 3 copy free.
Legend of Zelda: Skyward Sword No deal yet, but preorder through our link anyway, maybe you'll get a deal.
Amazon Kindle Fire Not so much a deal, but at $199 with all the feature this could be a nice iPad competitor.
Support the site and use one of the above links to order a game or three.
Also, if you find any other games with bonuses or credits post them here and I'll update the post.