I want build a GUI with gtk2hs, which will contain a lot of text (non editable) with a different formatting options for each piece of text. Is there any Gtk widget that was designed for this purpose? What kind of widgets are most appropriate for this?
you should use a GtkTextView widget that has been set as non-editable.
if the text is not overly long (a couple of short paragraphs) you can also use a GtkLabel, but if the length or number of the paragraphs get too big then measuring text will start to become a performance issue.