I went and played through the campaign again on Modern Warfare 2 and I noticed a couple things they could've put in multiplayer as killstreaks. They are...
11 kills- Operate a Mini-gun on a Black Hawk Helicopter (like on the end of Of Thier Own Accord)
15 kills- A Stryker APC will come and drive around the Vicinity of the map and the player can use the laser designater for the striker. now the only problem I see with this killstreak is maps like Highrise and Skidrow, where there is no road to drive on.
7 kills- MLRS barrage ( MLRS is Multiple Launcher Rocket System) I think it the Barrage seen on Exodus.
10 kills- This is not seen in the game at all but I think it would be a great thing to have. Call in a Warthog A-10 to spray the selected area with it's machine guns. ( Selected Area as in a pathway designated by the laptop computer seen ingame)
Well what do you guys think. If you have any other Killstreak ideas please share them. You never know, we could end up in a Black Hawk helicopter in MW3