I came across this list of of the 29 "healthiest foods on the planet" providing the best nutrition/calorie ratios...
FRUITS
01. Apricots
02. Avocados
03. Raspberries
04. Mango
05. Cantaloupe
06. Cranberry Juice
07. Tomato
08. Raisins
09. Figs
10. Lemons/Limes
VEGETABLES
11. Onions
12. Artichokes
13. Ginger
14. Broccoli
15. Spinach
16. Bok Choy
17. Squash
18. Watercress and Arugula
19. Garlic
GRAINS/BEANS/NUTS
20. Quinoa
21. Wheat Germ
22. Lentils
23. Peanuts
24. Pinto Beans
25. Low fat Yogurt
26. Skim Milk
SEAFOOD
27. Shellfish
28. Salmon
29. Crab
[For more complete info you can find the complete article
here ]