Until I tried it, I didn't know that you could open text files with QuickTime Player and watch the whole thing fly by -- very cool. You can use all the menu items, too -- View » Enter Full Screenange, change to another size, etc. For more control, choose Window » Show A/V Controls (Command-K), then use the Playback Speed slider to adjust how quickly the text goes by.
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robg adds: This works in both 10.4 and 10.5. It was noted in a comment by Kirk M. to
this hint, but I think it's worth running as a free-standing hint. The text scales perfectly as you resize the window, and each paragraph is one 'slide' in QuickTime Player. I couldn't get some text files to open, but most worked just fine.]