What do you mean by toggle comments? in the CSS files, you would use /* comment text */ and in a HTML file, you would use <! -- comment text --> to add a comment. Are you looking for a plugin to allow you to highlight text and then mark it as a comment?
I.e.
Code:
<!-- Write your comments here for a HTML file -->
/* This is a single-line comment in a CSS file */
p {
text-align:center; /* center the text */
}