Nature or artists usually do not stick to color theory to create an interesting color scheme. Jazz bands really start to swing when the drummer goes slightly off beat. If you restrict yourself to complementary colors, your choices are limited and the look of your presentation resembles those of many others who use the same approach.
Instead, get inspired by art (try Art Authority) or a or a colorful sea creature, or a photograph (check out Steve McCurry's blog) and upload the image to a color extraction tool such as Adobe Kuler. It will make you work more original, plus it adds a little personal secret to your presentation, your favorite painter or that memorable place that is hidden in the slides somewhere.