PowerPoint Template Design Tips
Before and After Magazine has a great,
free PDF download that shows you how to create compelling design cover patterns (even if you have limited design skills!)
This pdf file (requires Adobe Acrobat) is short, easy, well-written and well-designed....and it's totally free! You can use it as the author suggests -- to make report design covers -- but think about using some of his techniques for your PowerPoint templates, as well.