Android IceCream Sandwich 4.0 aka ICS is finally announced and its packed with features. Galaxy Nexus is the flagship device that would run ICS.
ICS basically brings Android 3.x Honeycomb features to phones. Lets go through the features quickly:

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30minutes Video demo of IceCream Sandwich

Android 4.0 ICS Features:

Updated Settings:  Revamped Settings screen organization. Items are arranged much better now.
Disabling Apps:  ICS adds the ability to disable an app outright. Don’t like an app that came preinstalled? Disable it! Its resources never run and its launcher icon is gone until you re-enable it.
Improved Download Manager.
Support for Encryption for Phones:  Honeycomb added full-device encryption, but ICS brings it to phones.
Audio Effects:  There’s a new audio effects API. Better media players coming!
New Font, Roboto: Droid Sans font is now gone for good.

OnScreen buttons, no hardware buttons: You dont need any hardware buttons for running ICS device, all the buttons: back, home are on-screen. Like Honeycomb, the buttons go invisible, smartly, to let you enjoy full screen video.
Resizable Widgets, Folders, Favorites: Dragging apps and contacts on top of each other create re-arrangeable folders. Users can stow their favorite apps, links, and folders into a new Favorites tray for quick and easy access
Screenshots: Hold down the power button and the volume down button to take a screenshot.
Notifications Revamped: Music controls have been integrated, and notifications can be dismissed by swiping
Improved Copy & Paste
Face Unlock
Enhanced Talk-to-Text: It’s more accurate.
Browser Tabs, offline: Upto 16 browser tabs. You can also save web pages offline
Gmail: Gmail now supports two-line previews, and sports a new context-sensitive action bar at the bottom of the screen. Gesture support allows you to swipe left and right between emails.
Contacts – People App: Contacts get re-vamped by showing contacts from Google+, Facebook, Twitter, etc.
Data Usage: You can now look at the details of what app is doing what with your data usage. Best part: The ability to limit data usage to a certain threshold.
Camera: Image stabilization, improved autofocus, and integration with other apps for sending photos or instant upload to Google+, built-in face detection, panorama and time lapse modes, and on-the-fly photo retouching and enhancements.
Android Beam: An secure NFC-powered sharing platform that lets users share nearly any kind of content, save for applications (in that case, a link to the Market is sent instead)