Sorry to bump this, but here's a better list of what ICS brings:
Option to use virtual buttons in the UI, instead of taking up capacitive touch buttons
Widgets are in a new tab, listed in a similar list to apps
Folders are much easier to create, with a drag-and-drop style similar to iOS
A customizable launcher
New phone app with visual voicemail functionality that lets you speed up or slow down voicemail messages
Pinch-to-zoom functionality in the calendar
Gmail has offline search, a two-line preview, and new action bar at the bottom
Swipe left or right to switch between Gmail conversations
Integrated screenshot capture by holding power and volume down buttons
Improved error correction on the keyboard
Ability to access apps directly from lock screen (similar to HTC Sense 3.x)
Improved copy and paste
Better voice integration
Face Unlock, a facial recognition service
New tabbed web browser, allowing up to 16 tabs
Browser now automatically syncs your Chrome bookmarks
Modern "Roboto" font
Data Usage section in settings lets you set warnings when you reach a certain amount of use and disabling data when you go over your limit
Ability to kill off apps that are using data in the background
Camera app: zero shutter lag, time lapse settings, zoom while recording
Built-in photo editor
New gallery layout, organized by location and person
Refreshed people app with social network integration, status updates and hi-res images
Android Beam, a NFC feature that lets you exchange websites, contact info, directions, YouTube, etc.
Don't like some of those preloaded carrier apps? Disable 'em. Android Engineer Dan Morrill mentions that, among other new features, any app can be disabled, and while it will still take up space in ROM, it won't be snatching any of your precious resources or clock cycles again if you don't want it to.
Really like the bolded parts. AFAIK, Sprint already allows you to do the last thing on the list, but Sprint's coverage doesn't work for me that well.
