I've been yammering about them for some time. To be honest, I didn't know what #5 should be, but as I've been deciding what foods should be "ubiquitized," leafy greens kept pooping up, finally taking their spot at #5.
Remember, I hate them, but I love what they can do for me.
Their best use for me is bulk. I can bulk out a canned soup, an omelet, a burrito, smoothie (green monsters, roaar!) or a meat entree with them. I up the nutritional value of any dish with them, without added effort. I also don't taste them, and when I add them raw, I lower the chances of destroying all of the water-soluble vitaminy goodness (vitamin C, B complex).
Another use: lazy side dish salad. Sometimes, I can't think of what I want to go with my meal, however, if I have some greens and haven't eaten enough veggies for the day, I put out some greens, lemon juice and fresh herbs (if I have on hand) or just salt & pepper, and I have a quick side dish.