by Max Chirkov on WordPress.org
Adds and option to lock post editor in HTML Mode on selected post types on per-item basis.

HTML Mode Locker settings under Settings => Writing.
We all experienced frustration of using WYSIWYG editor especially when switching between Visual and HTML modes. If you have a need to use Visual editor in your day-to-day operations, but you also need the ability to have some posts or pages in pure HTML format – HTML Mode Locker allows you to do that on per-post basis.