Adding a guideline to the editor in Visual Studio
This is originally from Sara's blog.
It also works with almost any version of Visual Studio, you just need to change the "8.0" in the registry key to the appropriate version number for your version of Visual Studio.
The guide line shows up in the Output window too. (Visual Studio 2010 corrects this, and the line only shows up in the code editor window.)
You can also have the guide in multiple columns by listing more than one number after the color specifier:
RGB(230,230,230), 4, 80
Puts a white line at column 4 and column 80. This should be the value of a string value Guides in "Text Editor" key (see bellow).
Be sure to pick a line color that will be visisble on your background. This color won't show up on the default background color in VS. This is the value for a light grey: RGB(221, 221, 221).
Here are the registry keys that I know of:
Visual Studio 2010: HKCU\Software\Microsoft\VisualStudio\10.0\Text Editor
Visual Studio 2008: HKCU\Software\Microsoft\VisualStudio\9.0\Text Editor
Visual Studio 2005: HKCU\Software\Microsoft\VisualStudio\8.0\Text Editor
Visual Studio 2003: HKCU\Software\Microsoft\VisualStudio\7.1\Text Editor
For those running Visual Studio 2010, you may want to install the following extensions rather than changing the registry yourself:
http://visualstudiogallery.msdn.microsoft.com/en-us/0fbf2878-e678-4577-9fdb-9030389b338c
http://visualstudiogallery.msdn.microsoft.com/en-us/7f2a6727-2993-4c1d-8f58-ae24df14ea91
These are also part of the Productivity Power Tools, which includes many other very useful extensions.
Without the need to edit any registry keys, the Productivity Power Tools extension (available for all versions of visual studio) provides guideline functionality.
Once installed just right click while in the editor window and choose the add guide line option. Note that the guideline will always be placed on the column where your editing cursor is currently at, regardless of where you right click in the editor window.
To turn off go to options and find Productivity Power Tools and in that section turn off Column Guides. A reboot will be necessary.
Visual Studio 2017 / 2019
For anyone looking for an answer for a newer version of Visual Studio, install the Editor Guidelines plugin, then right-click in the editor and select this:
Visual Studio 2022
Same author as the package above but seems he had to split the extension to work with 2022.
https://marketplace.visualstudio.com/items?itemName=PaulHarrington.EditorGuidelinesPreview&ssr=false#overview