Rumbler's there -- track down from the Steel Brigade Commander in the back row, and Rumbler is standing just in front of Sci-Fi and Slipstream.
There are a few I don't recognise:
I'm not overly familiar with the Sgt. Savage characters - I'm assuming they're all in the top-left, near Robo-JOE? I'm pretty sure Savage is the one with the green headband, but I don't know the guys to the left (naked bald guy; red headband guy; thick-set whit shirt guy) and above/right (smooth helmet & monocle-thing guy; JvC Heavy Duty look-a-like guy; round glasses & white headscarf guy). D-Day and Dynamite are amongst them, right? And are some of them from Extreme? (I don't like the idea of having Extreme characters in there since that was a totally seperate universe -- might as well have the Reloaded cast in there too, or at least the female Doc).
Who is the woman in white immediately below Robo-JOE? Not Storm Shadow's apprentice/girlfriend/enemy Junko Akita?
Then a couple of spaces below her is a guy with short, receding blond hair (surrounded by Sidetrack, Scoop, Pathfinder and Mace).
Just left of centre, above Spearhead and then Faces, is a smiling blond guy in a dark blue/black outfit. Maybe Daemon, the computer-guy Serpentor killed? He got more page-time than Cool-Breeze and Mangler put together, and they're on there.
Finally, an the far right edge about 2/3 of the way up, there's someone in black just above T'Gin-Zu, Red Spot and Wreckage. I can't even tell if it's meant to be a man or a woman...
I love the poster more in concept than execution -- the art could be WAY better. I can understand ignoring perspective a bit so the characters in back aren't too small to see properly, but a bit of consistency in scale should still be possible for guys standing next to each other; how huge is Doc, there...?! Shame they didn't get Tim Seeley to do it.
Here's hoping for a Cobra companion piece, with all the individual characters and maybe one each of the different troop-types...