Beans are often the staple of hard working but poor peoples' diets, because they are easy to grow and very full of energy. While this is great for a farmer or a blacksmith, this can make beans a rough thing for a sedentary modern worker to eat in quantity. Because the beans are full of instant energy - where modern workers rarely move around - eating them daily can lead to obesity.
Here are a few of the more common varieties of beans, with details on their nutrition.
Lentils give you 22g of net carbs per half cup. That's quite a lot! On the upside, they provide 22g of fiber in that same serving, so they are at least a good source of fiber. They have 16g of protein, which is why vegetarians often eat beans as their replacement for meat. They are not high in nutrition - they have 14% iron, but only 2% calcium and 2% Vitamin C. If you're not getting enough folic acid, they do have 90% folic acid.
Chickpea / Garbanzo Beans
Only 16g of net carbs per half cup, these are reasonably good for the bean family. They also provide 22g fiber in that serving, so another nice source of fiber. With 12% iron and 5% calcium they are not providing much nutrition-wise.
Pintos have a splotchy color, just like pinto horses have splotches on them. They are related to the kidney bean. They're 14g net carbs per half cup, with 7g of fiber along with that. Again, they provide iron and folates.
Kidney beans are also known as chili beans. They are used widely in southwestern cooking. The subject of many "fart jokes", it's wise to introduce kidney beans into your diet slowly to avoid gastrointestinal problems. Interestingly, this is related to a toxin in the beans - if you didn't cook the beans for at least 10 minute before eating them, you'd have even worse problems. They are 14g carbs per half cup, with another 7g of fiber in there.
Bean Carb Charts
Bean Sprouts Information
Lisa Shea's Library of Low Carb Books