What is new in ASP.NET 4.0

Check out new featueres in ASP.NET 4.0. Click on the link below to go to the detailed feature.

Core Services
   Web.config File Refactoring
   Extensible Output Caching
   Auto-Start Web Applications
   Permanently Redirecting a Page
   Shrinking Session State
   Expanding the Range of Allowable URLs
   Extensible Request Validation
   Object Caching and Object Caching Extensibility
   Extensible HTML, URL, and HTTP Header Encoding
   Performance Monitoring for Individual Applications in a Single Worker Process
   Multi-Targeting
Ajax
   jQuery Included with Web Forms and MVC
   Content Delivery Network Support
   ScriptManager Explicit Scripts
Web Forms
   Setting Meta Tags with the Page.MetaKeywords and Page.MetaDescription Properties
   Enabling View State for Individual Controls
   Changes to Browser Capabilities
   Routing in ASP.NET 4
   Setting Client IDs
   Persisting Row Selection in Data Controls
   ASP.NET Chart Control
   Filtering Data with the QueryExtender Control
   Html Encoded Code Expressions
   Project Template Changes
   CSS Improvements
   Hiding div Elements Around Hidden Fields
   Rendering an Outer Table for Templated Controls
   ListView Control Enhancements
   CheckBoxList and RadioButtonList Control Enhancements
   Menu Control Improvements
   Wizard and CreateUserWizard Controls 56
ASP.NET MVC
   Areas Support
   Data-Annotation Attribute Validation Support
   Templated Helpers
Dynamic Data
   Enabling Dynamic Data for Existing Projects
   Declarative DynamicDataManager Control Syntax
   Entity Templates
   New Field Templates for URLs and E-mail Addresses
   Creating Links with the DynamicHyperLink Control
   Support for Inheritance in the Data Model
   Support for Many-to-Many Relationships (Entity Framework Only)
   New Attributes to Control Display and Support Enumerations
   Enhanced Support for Filters
Visual Studio 2010 Web Development Improvements
   Improved CSS Compatibility
   HTML and JavaScript Snippets
   JavaScript IntelliSense Enhancements
Web Application Deployment with Visual Studio 2010
   Web Packaging
   Web.config Transformation
   Database Deployment
   One-Click Publish for Web Applications
   Resources 
 

Here is the detailed document.
http://www.asp.net/learn/whitepapers/aspnet4/