One post production technique for delighting the viewer's eye is to first convert the image to B&W, then restore bits of color. The element of surprise is often stimulating.
For this shot of a "formerly yellow nasturtium," I applied the Black & White adjustment in Aperture 3.3. Then, in the Black & White Adjustment Brick, I clicked on the gear menu, and selected, "Brush Black & White away." I used an adjustment brush to restore color to the nasturtium leaves. I like the pattern they form around the flower.
The first pass took only a few minutes of image editing. If, after time, I decided that I liked the photo, I would go back and spend another 20 minutes or so touching up the details. Typically, I "live with a photo" for a day or two before deciding whether or not to put more work in to it.
This technique works well for greeting cards and personal messages. It shows that you put a little extra effort into the image that you're sharing.
You can find more photo tips and "photography how tos" on my Pinterest page.