Probably the best food you can put in your body, bar none.
It depends what you like. Most people don't care for organ meats, which is why they're so cheap. In general, any of those organs from cattle/bison, sheep, goats, pigs, or poultry are great. My favorite liver is bison liver (you can order it online, but it's $10 for 8 ounces, not so cheap.). Those of you who prefer something closer to steak, try any kind of heart. Beef heart is great and super cheap ($1 lb or less?), but lamb/sheep heart is my favorite. I've got some kidney in my freezer, but I haven't gotten into it yet-- since I enjoy liver, heart and tongue-- that pretty much covers my nutrient needs.
Grass fed animals, typically beef. The nutrient density is off the charts. When I eat dessicated beef liver (available in pill form), the code just flows out of me...
It's not cheap unfortunately, feedlot beef and chicken muscle meat is typically cheaper than grass fed beef liver.
