Lodge and Camp chef both are making conventional camp style dutch ovens. These have a lip around the lid and three short legs on the bottom of the pot. Use these primarily for cooking with charcoal or a wood fire, where embers can be spread beneath the pot and around the top of the lid. Lodge had the only mainstream camp ovens for a while; Camp Chef was making a hybrid, which they still do. Only recently did Camp Chef start casting pots similar to the Lodge product, though the general concensus is that Camp Chef QC may not be as good as Lodge on these traditional styles. In any case, Lodge is most likely the brand you will find most often. In fact, Walmart even stocks them. The most common size is what's called a 12", either as a regular depth (6 quart) or as a deep pot (8 quart). These are the most popular, and I have more in this size than any other, and I tend to use them more than the rest. Most dutch oven recipes call for one of these two sizes, so it is a good place to begin.

You will find Lodge in all the big name sporting goods chains, like Bass Pro, Cabelas, Sportsmans, Gander Mountain, etc. Check the Lodge website to see what you can expect for pricing roughly, and to get an idea what you are looking for at a store.

I have pots ranging from 4" diameter to 20", Most often, I find myself reaching for the 12s, both at home and camp. At most Dutch Oven gatherings, about 60% of the pots are going to be 12". Like I said, it is a good place to start.

Probably the single best website for you to find more information is at IDOS.org. Pretty much everything you could ever need or want to know about cast iron cooking is there, and more people willing to offer you advice than you would care for.