Courtney and I eat meat. We are carnivores. But as carnivores go, we are pretty bad at it. We have frequently committed to a week of vegetarian cooking, or a month of eating meat only once a week (if you count farm raised clams and wild Alaskan salmon as vegetables). We also cook vegan meals from time to time. Why do we do this? Because no matter how much you love meat, you have to recognize that eating large amounts of beef for every meal is not a sustainable practice.
Buying grass finished beef is a little better, but it is very expensive compared to conventional beef. Vegetarian cooking, on the other hand, is significantly cheaper than the cheapest meat. Removing meat from just a few meals a week can greatly improve your food budget. If you are not going completely vegetarian, the health risks (low iron or protein intake) are negligible, especially if you eat beans, legumes, nuts or a meat replacement (tofu, e.g.) with each veggie meal.
Another excellent source of iron is clams, mussels or oysters. Farmed, these delicacies are also highly sustainable. There is nothing simpler than steaming clams in some white wine, with chopped onion and parsley and a little butter. They can be served in their shells with the steaming broth. Clams usually have more iron than similar amounts of beef (note: canned clams may have significantly lower iron content, fresh farmed are best).
If you are going for a vegan trial, however, more planning is required. The two main concerns are how to get the nutrition you need and how to make tasty food. Well, in the taste department I have two bits of advice: oil and sea salt. A lot of the flavor of meat comes from the natural salt and fat content, and when switching to a no meat diet doubling the salt and adding a little extra oil can go a long way. Sea salt specifically contains a number of things which are basically impurities that mimic meat flavor (the blood of most animals is similar chemically to sea water).
Another tip on vegetarian cooking: roast your vegetables. A little browning is vital to a complex flavor without meat, and a little black won't hurt either. Combined with the sea salt, this technique will produce a savory flavor that will make you forget about the lack of meat.
Finally, mushrooms are great in meatless dishes. They provide some texture, some body, and although I think white mushrooms are pretty flavorless, most varieties provide a rich umami flavor that is otherwise hard to come by without some animal product involved.
In terms of nutrition, the biggest concern aside from iron is protein, and for this beans are your best bet. Canned or dried, mashed or whole, beans and other legumes are packed with protein, low in fat and even have some fiber. They tend to soak up whatever flavor is around, so I usually add beans right at the end, otherwise everything else in the dish will lose its flavor.
In the interest of full disclosure, I feel I should tell you that while writing this post, I was planning, preparing, cooking and eating hamburgers. What can I say? I told you I was a carnivore. Besides, it was sunny all day today, and there probably won't be another good day to BBQ until spring. I did use grass fed beef though, and it was the first time that we cooked meat in a week, so I can't feel too bad.