Resharper (or R#) is an absolute gem of a tool. After using it for a year, I really don’t know how I got along without before. If you write code in .NET (C# or VB.NET), you owe it to yourself to try it out. Version 4.0 was the first to support C# 3.0:
ReSharper 4 Full Edition and C# Edition extend language support to C# 3.0, including LINQ, implicitly typed locals and arrays, extension methods, automatic properties, lambda expressions, object & collection initializers, anonymous types, expression trees, and partial methods. ReSharper not only analyzes the new constructs, but provides C# 3.0-related enhancements in a number of areas — specifically, warnings, suggestions, code completion options, refactorings, and templates.
The guys at Jetbrains just released versus 4.1. They offer a free thirty-day trial over at http://www.jetbrains.com/resharper/ – do it!