Take a look at this shot from Death Valley National Park in California. What makes it so striking? Well - first off all, orange and blue are complimentary colors - that is, they are located directly across from one another on a color wheel. When complimentary colors are placed side-by-side, they seem to become more vibrant. The contrast between the colors in the image above seem to grab you and demand your attention. This image is even more eye-popping because of the rich, side lighting which enhances the golden sand and the beautiful rippling patterns.
Here's another example of complimentary colors in photography. This beautiful, red Columbine flower (Great Smoky Mountains National Park, Tennessee) stands out beautifully against a complimentary background of fresh, green foliage.
Use complimentary colors to really make an image pop - and to call attention to an important element in your photo.