How do you reset the Zoom in Visual Studio 2010 and above
There's a zoom control in the bottom-left of the code editor. You can pick 100% from there, or type it by hand.
You can try VSCommands extension from Visual Studio Gallery, it adds several new features around zooming in VS2010
In Visual Studio 2015/2017/2019 (easy to miss if using a dark theme):
There is a select box for this at the bottom left of the editor window - choose 100% ;)
I was unable to find a keyboard shortcut for it, though zooming in and out can be done using Ctrl + > and Ctrl + <.
Please note the horizontal scroll bar must be turned on to see the zoom level.
Tools / Options / Text Editor / All Languages / Scroll Bars
Another option (Visual Studio 2013/2015) is to use Ctrl with the mouse wheel (up to zoom in, down to zoom out).