What's new in ASP.Net 3.5

One major improvement for Visual Studio 2008 over earlier versions is you can specifically choose the .NET Framework version for an application, allowing it to be used for older .NET 2.0 applications as easily as .NET 3.5 applications.

ASP.NET AJAX

LINQ

There are a number of new controls added to the ASP.NET environment that simplify the display of data on a Web page, as well as provide the user with more flexibility in viewing and selecting data. While ASP.NET 2.0 added several controls for working with data on the Web (notably GridView, DetailsView and FormView), they were restricted in their capabilities and flexibility. Two new controls, ListView and DataPager, are new in ASP.NET 3.5 and are extremely useful.

Support for several standard protocols has been added to ASP.NET 3.5, too. The most common protocols now supported are SOAP (a protocol for moving XML messages, SOAP is a foundation of the Web services protocol stack), RSS (Web feed format for frequently-updated content), JSON (JavaScript Object Notation, a data interchange format), and POX (Plain Old XML, which is actually XML with other specifications such as XML Namespaces, XInclude, XLink and Dublin Core.

ASP.NET 3.5 includes the ASP.NET MVC

New in .NET framework 2.0

It brings a lot of evolution in class of the framework and refactor control including the support of

Generics
Anonymous methods
Partial class
Nullable type
The new API gives a fine grain control on the behavior of the runtime with regards to multithreading, memory allocation, assembly loading and more
Full 64-bit support for both the x64 and the IA64 hardware platforms
New personalization features for ASP.NET, such as support for themes, skins and webparts.
.NET Micro Framework

New in .NET framework 3.0

Also called WinFX,includes a new set of managed code APIs that are an integral part of Windows Vista and Windows Server 2008 operating systems and provides

Windows Communication Foundation (WCF), formerly called Indigo; a service-oriented messaging system which allows programs to interoperate locally or remotely similar to web services.
Windows Presentation Foundation (WPF), formerly called Avalon; a new user interface subsystem and API based on XML and vector graphics, which uses 3D computer graphics hardware and Direct3D technologies.
Windows Workflow Foundation (WF) allows for building of task automation and integrated transactions using workflows.
Windows CardSpace, formerly called InfoCard; a software component which securely stores a person's digital identities and provides a unified interface for choosing the identity for a particular transaction, such as logging in to a website

New in .NET framework 3.5

It implement Linq evolution in language. So we have the following evolution in class:

Linq for SQL, XML, Dataset, Object
Addin system
p2p base class
Active directory
ASP.NET Ajax
Anonymous types with static type inference
Paging support for ADO.NET
ADO.NET synchronization API to synchronize local caches and server side datastores
Asynchronous network I/O API
Support for HTTP pipelining and syndication feeds.
New System.CodeDom namespace.