There is nothing better than a tool that works. Here is a listing of tools that I use.

ReSharper
Excellent Visual Studio Plug-in.
Cost: $149/$249

CodeRush
Visual Studio Add-in. Works well with ReSharper.
Cost: $249

Subversion
Version Control System. Provides excellent range of features and used by many organizations and companies.
Cost: Open Source

TortoiseSVN
THE Subversion interface for Windows systems. If you download one tool for Subversion, this has to be it.
Cost: Open Source

VisualSVN
Great Visual Studio plug-in that allows Subversion integration. Uses/Requires TortoiseSVN.
Cost: $49

MbUnit
Unit Testing Framework for .NET.
Cost: Open Source

NAnt
.NET Build Tool. Create automated build scripts for your application. Build in one step.
Cost: Open Source

CruiseControl.NET
Continuous Integration server for .NET.
Cost: Open Source

NHibernate
An ORM (Object/Relational Mapper) based on Java's Hibernate.
Cost: Open Source