Use a label widget -- its not restricted to just displaying of single lines of text. Combined with pango markup it can do all sorts of useful formatting for jobs such use in on screen reports. If you set the right flags, you can also copy the contents the clipboard for pasting elsewhere. If it gets really big, add it into a scrolling window.
PS> Here's an example of one of my apps which uses a GtkLabel to display the results of a dictionary search. Setting colour attributes with a Pango string is much more convenient than creating tags and inserting strings into a text buffer.