ASP.NET 4.5 New Features List

• ASP.NET Framework and Runtime
  • HTTP Requests and Responses with  Asynchronously Reading and Writing  supports
  • HttpRequest handling Enhancements.
  • Asynchronously flushing support for response
  • giving Support to Task-Based and  await  Asynchronous  Handlers and Modules
  • Asynchronous HTTP modules enhancements
  • Asynchronous HTTP handlers  enhancements
  • ASP.NET Request Validation Enhancements.
  • Deferred ("lazy") request validation Enhancements.
  • unvalidated requests support
  • AntiXSS Library support
  • WebSockets Protocol Enhancements and support
  • Bundling and Minification support or enhancements.
  • Web Hosting  Performance Improvements for 
    • Key Performance Factors Enhancements.
    • Requirements for New Performance Features  Enhancements.
    • Sharing Common Assemblies  Enhancements.
    • Using multi-Core JIT compilation for faster startup  Enhancements.
    • Tuning garbage collection to optimize for memory  Enhancements.
    • Prefetching for web applications  Enhancements.
• ASP.NET Web Forms
  • Strongly Typed Data Controls Enhancement
  • Model Binding New Features
    • Selecting data Feature
    • Value providers Feature
    • Filtering by values from a control Feature
  • HTML Encoded Data-Binding Expressions Enhancements
  • Unobtrusive Validation Enhancements.
  • HTML5 Supports for updates.
• ASP.NET MVC 4 Supports and Enhancements.
• ASP.NET Web Pages 2  Supports and Enhancements.
• Visual Studio 11 Beta Enhancements.
  • Project Sharing Between Visual Studio 2010 and Visual Studio 11 Beta (Project Compatibility) Enhancement.
  • ASP.NET 4.5 Website Templates  Configuration Changes
  • IIS 7 for ASP.NET Routing  Native Support
  • HTML Editor Enhancements.
    • Smart Tasks  Enhancements.
    • WAI-ARIA support or Enhancements.
    • New HTML5 snippets Enhancements.
    • Extract to user control Enhancements.
    • IntelliSense for code nuggets in attributes  Enhancements.
    • Automatic renaming of matching tag when you rename an opening or closing tag  Enhancements.
    • Event handler generation  Enhancements.
    • Smart indent  Enhancements.
    • Auto-reduce statement completion  Enhancements.
  • JavaScript Editor Enhancements.
    • Code outlining  Enhancements.
    • Brace matching  Enhancements.
    • Go to Definition  Enhancements.
    • ECMAScript5 support and   Enhancements.
    • DOM IntelliSense Enhancements.
    • VSDOC signature overloads Enhancements.
    • Implicit references Enhancements.
  • CSS Editor Enhancements.
    • Auto-reduce statement completion Enhancements.
    • Hierarchical indentation Enhancements.
    • CSS hacks support and  Enhancements.
    • Vendor specific schemas (-moz-,-webkit) Enhancements.
    • Commenting and uncommenting support and  Enhancements.
    • Color picker Enhancements.
    • Snippets support
    • Custom regions Enhancements.
  • Page Inspector Enhancements.
  • Publishing Enhancements.
    • Publish profiles Enhancements.
    • ASP.NET precompilation and merge Enhancements.
• IIS Express Enhancements.

For more information please see this link