Please find below some of the important links which have been collated on Microsoft Core .NET Platform.

.NET Framework Conceptual Overview
The .NET Framework has two main components:  the common language runtime and the .NET Framework class library.
The common language runtime is the foundation of the .NET Framework.

About Microsoft .NET 3.5 Framework
Microsoft .NET Framework version 3.5. Framework is an integral Windows component that supports building and running the next generation of applications and Web services. The key components of the .NET Framework are the common language runtime (CLR) and the .NET Framework class library, which includes ADO.NET, ASP.NET, Windows Forms, and Windows Presentation Foundation (WPF).

.NET Framework 3.5 Architecture
The architecture of the .NET Framework version 3.5 and 3.5 Service Pack 1 (SP1) builds upon the earlier versions of the .NET Framework.

.NET Framework System Requirements
 - System Requirements for Version 3.5
 - System Requirements for Version 2.0 
 - System Requirements for Versions 1.0 and 1.1

Official downloads
Microsoft .NET Framework 3.5 Service Pack 1
.NET Compact Framework 3.5 Redistributable
Windows Installer 4.5 Redistributable
Microsoft .NET Framework 3.0 Redistributable Package
Microsoft .NET Framework 2.0 Service Pack 1 (x86)
Microsoft .NET Framework Version 2.0 Redistributable Package (x86)
Public Sector Developer Weblog
Download the .NET Framework 3.0 Runtime Components
.NET Compact Framework API Documentation
ActiveSync 3.7.1
Windows Mobile-based Smartphone 2003 SDK
Introducing the .NET Micro Framework
Building Devices for Windows SideShow with the .NET Micro Framework
Porting the .NET Micro Framework 
.NET Compact Framework Downloads 


BCL Team Blog

Community Blogs

Aaron Ruckman's Web Log

Wenlong Dong's Blog

Wikipedia - .NET Framework


Standardization and licensing

.NET Framework 3.5

.NET Framework 4.0

.NET vs. Java and Java EE

Microsoft .NET new logo and branding

.NET Framework Developer Center

.NET Framework Technologies
Data Platform Development using ADO.NET

Getting Started with ASP.NET

Base Class Libraries Community

.NET Micro Framework

Windows CardSpace

Windows Communication Foundation

Windows Client.NET

Windows Workflow Foundation

.NET Framework 4.0

Parallel Programming with .NET:.NET Framework 4.0 Poster for Download

Sandboxing in .NET 4.0

Tools and Utilities
.NET Tools and Utilities

WPF Toolkit

What build tools are available for .NET?

CLR Profiler for the .NET Framework 2.0

Fx Cop

Performance Console (PerfConsole) 1.0

.NET Productivity Suite



CLR Profiler

Windows Communication Foundation Tools

Windows Presentation Foundation Tools

Windows Workflow Foundation Tools