The highest killstreak possible that you can earn is 11. There is nothing higher, as well as no nukes like Infinity Ward had in Modern Warfare 2 nor will there be anything similar to such.
Also, kills earned these killstreaks will not count towards increasing your killstreak. For example If you are running with Valkyrie Rockets, and kill a few enemies, it will not earn you a Chopper Gunner.
3 killstreaks: Spy Plane, RC-XD
4 killstreaks: Counter-Spy Plane, SAM Turret
5 killstreaks: Care Package, Napalm Strike
6 killstreaks: Sentry Gun, Mortar Team
7 killstreaks: Attack Helicopter, Valkyrie Rockets
8 killstreaks: Blackbird, Rolling Thunder
9 killstreaks: Chopper Gunner
11 killstreaks: Attack Dogs, Gunship