I searched, but didn't find anything posted about this. Please notify me if I am mistaken.
The information on the CoDBlackOpsNews website state that the highest kill-streak in the game is 15. Kill-streaks
will be customizable, as in Modern Warfare 2.
Kill-streak kills will not contribute to your kill-streak, you will have to get them with your main weapons, alone.
Some kill-streaks may not require you to not die, but rather be unlocked when you just acquire the necessary amount of kills for said kill-streak. So, basically, not all of them are necessarily 'kill-streaks'.
Game-ending streaks have been removed
UNCONFIRMED = speculation or independent research.
3 Kills is the Remote Controlled car / UAV. (UPDATE: The UAV may as well be the SR-71, but maybe the SR-71 is capable of shooting, too.)
4 kills is a care-package / HIMARS. (High Mobility Artillery Rocket system. You can see this in the video, a missle comes almost straight towards the guy, rather than from above.)
5 kills is perhaps the 'Archangel' / UNCONFIRME

Dogs. (Not overkill, though.)
As seen in the video.
15 kills, but more possible different kill-streaks.
Sources:
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[ame=https://www.youtube.com/watch?v=h_fsM6LBi54]YouTube - Call of Duty: Black Ops - Multiplayer Teaser[/ame]