EditorConfig - Reads your .editorconfig files and applies their settings.
Markdown Editor - Edit Markdown with live preview.
Smooth Scrolling - Use smooth scrolling instead of jumpy scrolling, nice for two-finger touchpad scrolling. There are also two different extensions named "Smooth Scroll" (no "ing") that do similar things. I've had one or another of these work better depending on the machine.
Strip'em - Force consistent newlines when files are saved. (Note this is not in the extension gallery, you have to get it from the developer's site.)
TabSanity - For projects that insist on spaces for indentation, makes the left and right arrow keys jump a full indent level instead of one space.
Text Macros for Visual Studio 2012/2013/2015 - Adds some of the keyboard macro support that went AWOL some years ago.
And of course things like ReSharper or Visual Assist, plus language specific extensions like HLSL Tools, PowerShell Tools, Python Tools, etc.