Phones that will most definitely get the upgrade.
Galaxy S2 lines and S3, (S4 coming soon)
All HTC released in late 2011 to 2012
All Droids(Razr etc.) released in late 2011 to 2012
In fact most Android Phones that are Made in late 2011 coming to 2012 will get the upgrade, Especially Top Brands like HTC,Samsung, and Motorola.
I have the Galaxy s2 Epic Touch 4g and am already running Android 4.0 that samsung put up as an update OTA. So I believe most of these phones will get the update.
Now lets talk about the phones that will need root to get the update.
-Note, I have a Droid Eris from 2007 running CM7 Android 2.3.7
All the Galaxy S1 lines-most likely-(i have the galaxy s epic 4g running CM9)
HTC Evo 4g(maybe), shift,design, and 3D
Droid 2 and a few others
Most likely all android phones that has developers working on it will receive the update.
-Themer and Dev from Xda-developers.com