I was first introduced to the idea of eating alkaline foods reading Politically Correct Nutrition, but didn't quite understand the significance. Kevin Tudreau states it is a natural remedy; the more alkaline we are the better able we will be to fight off disease. The more acid our bodies are, the more susceptible to illness we becomes.
Here's a list of alkaline foods from energize.com. However, here's another list from rense.com which contradicts it, at least for lentils, so(?).
Clean Up Your Diet by Max Tomlinson lists "asparagus, onions, parsley, broccoli, garlic, okra, squash, green beans, celery, lettuces, sweet potatoes, zucchini, lemons, limes, grapefruits, mangoes, papayas, figs, kiwis, apples, pears, and all kinds of melon" as alkalizing foods.