What useful plug-ins / debuggers for Visual Studio do you use (for Windows)?

P.S. I know Visual Studio has a good debugger)

Keep in mind I and the gang don't add anything that didn't come with VS. So the answer is none.

But external to VS we do use WinMerge from time to time.

I used to use the Regular Expression plugin until I rolled my own stand-alone tester.

commented: Great! I looked at this plugin. I did not know about it. I don’t often work with regular expressions, this plugin can be really useful to me sometimes +0

Can you clarify what do you need? What technologies are you associated with? Different plugins can be used for different projects. There is a rich selection of plug-ins in Visual Studio

commented: Detailed reports, resource usage, VCS as rproffitt said... +0

I really like GitHub Extension for Visual Studio. This plugin is available in the extension store for visual studio. It is free, you do not need special requirements.
Markdown Editor is quite popular. Many friends use it.
As for

Detailed reports, resource usage

I can't advise anything

I have been using Visual Assist for over 15 years. A few years ago, I tried turning it off and using plain Visual Studio, but it didn't take long to realize I preferred many of the little things that VA does to make programming quicker and easier.