Internet Explorer 10 Dev Preview 3 (blogs.msdn.com)

They've added:

Cascading Style Sheets (CSS) Advanced Layout

   CSS Regions
   CSS3 Multi-column Layout
   Flexible Box (“Flexbox”) Layout
   Grid Alignment
   Positioned floats

   CSS3 3-D Transforms
   CSS3 Animations
   CSS3 Gradients
   CSS3 Transitions
   CSS3 Text
      The text-shadow property
   Hyphenation

   Panning and Zooming
   Removal of style sheet limits

Document Object Model (DOM) support

   Advanced Hit Testing APIs
   CSSOM Floating Point Value support
   Media Query Listeners
   Pointer and Gesture DOM events

ECMAScript 5 (ES5) support

   The strict variant of ECMAScript (“ES5 strict mode”)

F12 Developer Tools (Not available in Metro style apps.)

Improved support for workers

HTML5 support

   Asynchronous Script Execution
   Application Cache ("AppCache")
   Drag and Drop
   File API
   Forms Validation
   Progress and Range Control
   History
   Parsing
   Sandbox
   Web Workers
   Channel Messaging
   Web Sockets
   Spellcheck

   Indexed Database API ("IndexedDB")
 
   SVGSVG Filter Effects

   Web performance APIs