i found this handy site tonight that allows you to compare the nutritional values of two different foods side by side. their index has a huge quantity of foods list so it's possible to compare pretty much anything you want or get close to it. they also have some great top 10 type lists, including one for the top 10 food sources of protein.
top 10 list:
http://www.healthaliciousness.com/most-nutritious-foods-lists.php
food comparison table:
http://www.healthaliciousness.com/nutritionfacts/instructions.php
We don't know what our limits are, so to start something with the idea of being limited actually ends up limiting us.
Ellen Langer