Storing html in mysql text fields, or include files? (html formatted articles)
I would recommend you put as little HTML in your database as possible. One very popular design pattern for websites is the Model-View-Controller pattern.  

Using that pattern your data (author, title, categories, article content, etc.) would be stored in the database without HTML tags and be called the Model.  Then the structure of the HTML page would be stored in a file called the View.  The Controller would be in charge of accepting the HTTP requests, requesting the appropriate data from the database, and merging/sending that data with/to the view.  

Any common web programming platform should be able to accommodate this pattern.