I also think Presentation Zen is hot. I found it very useful and I am recommending as a great guide to developing Ballroom Style presentations.
Here are three guidelines from the book that will make a huge difference in the quality of your Ballroom style presentations:
1. Full-sized images (p. 138). Use high resolution images that bleed right off the edge of your slides, to fill the entire screen. This takes full advantage of your display space, and it seems to me that--all other things being equal--higher resolution images are more attractive and emotionally appealing.
2. Empty space (p. 146). Don't feel compelled to fill every slide. When you're not using a full-slide image as in point #1 above, use lots of white space so that your content will stand out.
3. Contrast (p. 153). Use high contrast colors (i.e. don't be afraid of black and white) so that your content will be displayed clearly.
Just a small selection of lots of good stuff in this book.