Here are a few new tools that I have been using over the past few months which are all very useful. Thanks to my colleague Neil Schulman for recommending ReSharper which is a C# refactoring and intelligent code assisting tool which integrates with Visual Studio 2005. ReSharper is great for showing where errors exist in your code and pointing out where optimizations can be made. ReSharper also has extended Visual Studio intellisense capabilities which alone are worth the install. I personally love the closing brace identifier feature which highlights the closing or opening brace for any that you click on.
Another tool I have been using to assist with my BizTalk SFTP adapter work has been FileZilla. Many of you may already be familiar with this handy opensource FTP utility which provides the ability to do SFTP transfers as well!
Thanks to Marina for recommending SmartAssembly which looks to be a useful .NET obfuscation tool although I haven't yet given it a try :)