MVC & Razor

Data Attributes - Control MVC behaviour from the Data definition
Dynamic Dropdowns - Use DropdownListFor in Scaffolded Views

IoC and Unit Testing

Unit Testing With Moq - a tutorial I wrote for Haven Power
IoC and StructureMap - Inversion of Control pattern using StructureMap

Object Relational Mappers (ORMs)

Entity Framework:
  Code-First Annotations - Define database properties from data model
  Code-First Fluent API - Define database properties in code using Fluent API
  Code-First Complex Objects - Complex objects and their database implementation
  Lazy Loading - Deferred execution of sub-class queries
  Table-Per-Type - Class inheritance database implementation
  Table-Per-Hierarchy - Class inheritance database implementation
  Table-Per-ConcreteClass - Class inheritance database implementation

nHibernate:
  nHibernate - An alternative ORM solution

AJAX

C# AJAX - How to use AJAX on your C# pages
ScriptManager - Using ScriptManager to access Ajax methods
Homebrew - How to use AJAX on any HTML page

Javascript

dHTML - Cross Browser DHTML functions
Google maps - How to use Google Maps API
Draggable Objects - How to drag and drop in browsers
Cookies in Javascript - How to set and retrieve

C# Goodies

User XML in web.config - How to insert your custom XML data into standard web.config
C# Attributes - Using standard and custom Attributes in C#
UI Threading - Allow Threads to Communicate with the UI - Threads using Delegates
Pretty XML - Quick way to format an XML string with indents, line breaks etc
LINQ to Objects - C# LINQ to Object simple selects and joins
Custom Iterators - C# Using yield to product custom object iterators
Operator Overloading - C# Overloading standard operators and methods
Custom Casting - C# Providing custom type conversion methods
Themes and Skins - C# Themes and Skins for asp.net controls

Services

C# REST services - Implementing RESTful resources as URIs in C#
WCF in C# - WCF Services Using HTTP and TCP Endpoints