Call of Duty 4: Modern Warfare and Call of Duty: World at War are both 50% off during the duration of Ghosts being a showcase on the front page of Steam, so be sure to pick up a copy of both ASAP.

Call of Duty 4: Modern Warfare ($10 USD)
http://store.steampowered.com/app/7940/

Call of Duty: World at War ($10 USD)
http://store.steampowered.com/app/10090/

Don't forget both have mod tools and tons of custom maps and mods still being made! Be sure to join the Call of Duty User-Generated Content Group

Please check out and consider joining a new group for playing maps and mods for Call of Duty 4, World at War, and Black Ops.

http://gtm.steamproxy.vip/groups/CoDUGC

Have fun playing the latest maps and mods being made by the community while also helping content creators get some feedback on their work.

Thanks,
SparkyMcSparks

http://store.steampowered.com/sale/mwm_cod?snr=1_41_4__42

Redeploying with an arsenal of content unlike any in franchise history, Call of Duty®: Modern Warfare® 3’s first downloadable “Collection” arrives stockpiled with not only four Multiplayer/Survival Mode Maps, but two Special Ops Missions—the first time Call of Duty® has ever made Special Ops downloadable online.

Armed with just this one content pack, players can choose between heading to a militarized Central Park in Liberation, destroying scenic vistas in a seaside Italian getaway in Piazza, raining glass on New York passersby from 70-stories-up in Overwatch, and battling beside a downed Air Force One in Black Box.

As if that breadth of multiplayer variety wasn’t enough, fans of Special Ops can hop aboard snowmobiles to infiltrate a diamond mine in Black Ice or head to India, where Negotiator will leave the fate of hostages in their hands.

In a class of its own with half-a-dozen forms of content, Modern Warfare® 3’s first downloadable “Collection” offers a range of combat and co-op the likes of which has never been seen before.


Source: http://store.steampowered.com/app/42695/

"Activision will be hosting a Free Weekend for Call of Duty®: Modern Warfare® 3! Pre-load the game now and be ready to play when the free weekend starts on Thursday, February 16th at 10am Pacific Time.

Click here < steam://install/42690 > to start pre-loading, or visit www.steamgames.com/about to install Steam.

The Free Weekend of Call of Duty®: Modern Warfare® 3 will let you play the entire multiplayer portion of the base game."

Source: http://store.steampowered.com/news/7346/