Absolute HTML Compressor optimizes HTML files, so they're smaller.
Often, compressing HTML files can cause corruption, but Absolute HTML Compressor claims to have solved that problem.
Usage is cut and dry. Select an HTM or HTML file or folder including subfolders and click compress. Be sure to check under options to backup or backup manually yourself just in case. Command-line is supported for the geek who wants to go old school.
Other options are also worth a look. Some of the possibilities include merge lines, remove unnecessary whitespace, remove unnecessary quotation marks, and more.