There is of course one particularly famous farm model out there: Polyface Farm, the creation of Joel Salatin. Joel seems to have become the de facto spokesperson for small-medium scale farming (he's featured in the Omnivore's Dilemma, Food Inc, etc) and in many ways, he is a good one. Joel built a very successful farm from the ground up, starting with only his ingenuity and the land he inherited from his father. If you've read You Can Farm (and I highly recommend it. It's a great book) you can understand that he spend years living in poverty conditions before the farm business really took off to the point where it was making a reasonable amount of money. Now, he gets a lot of income from speaking fees, but the farm seems to be going strong. The hardest part of using Joel as your farming model is that is next to impossible to emulate Joel Salatin: he has a knack for marketing that most of us introverted farm types will never develop, and as I mentioned above, he started with land that he owned AND worked many years living in poverty. Lastly, when you dig deeper into some of his farming practices, it is easy to find things that one may not agree with (using Cornish Cross chickens, for instance, or trucking in huge amounts of feed). Nonetheless, he is a great model, but he doesn't share the nitty gritty of his farm economics (although he sort of does in his books).
There are also lots of local farms in the Northwest that have been around for a seemingly long time. The larger ones are so far removed from the kind of farming I'm interested in that it's not very helpful to look at them as a model. I have no interest in running a huge business that takes me completely out of the fields. A lot of dairies are smaller, but the co-op model that most dairies use is a bit of a special case, and I have no interest in milking cows, so I push them off to the side. That leaves us with farms that do most of all our their sales through direct marketing. These are the farms that go to farmers markets, or have a CSA, or have a website based distribution hub. Most of the farms that I am aware of our predominantly "mixed vegetable" farms, meaning that they grow a wide variety of vegetables and sell them fresh to people through CSAs, farmers markets, roadside stands, and to restaurants. There seem to be some larger operations in Eastern Washington that seem fairly successful, but those economics are so different from here that it's not a very useful model. There are a few big operations in Western Washington too. I'm most familiar with Full Circle (no longer Full Circle Farm) which is based in Carnation. I've been to that farm a few times now, and I have a good idea of the operation. It's big. And it has now branched out to being more than a farm--now distributing food grown locally with food from all over the world. Mixed vegetable farming is very labor intensive, so most of the bigger farms presumably use cheap migrant labor, and the smaller ones either use an army of apprentices (which is really the same thing) coupled with a very overworked farmer/owner. There seem to be quite a few of these smaller mixed vegetable farms in the area, but I'm not convinced that the economics are such that one can stay small, make enough money, and not get burnt out in very short order.
There are also quite a few small-medium farms that concentrate on direct marketed meat production. These farms tend to be similar to Polyface. I don't have insight into their economics, so I can't really use them as a model. With animals, land prices become a big limiting factor because you simply can't produce as much revenue in a small space as you can with mixed vegetables (unless you run a CAFO, but let's not even go there).
There are also quite a few farms that do a combination of food production and agri-tourism. I have a few bits of insight into these types of models, and from what I have gleaned, the agri-tourism part tends to be the dominant source of income. I've been focused in on making a living from food production only (at least to start), so I can't use these farms as models either.
Plenty of small farms utilize a second source of income from a part-time job or spouse that works full time (like mine, at the moment!) Clearly, this is not a model for farm-based economic independence. It may turn out to be the only viable way of having a small farm and a comfortable lifestyle. If the time commitment is small enough that the farmer is not overwhelmed (or the spouse doesn't become , then it might be worth it.
If you're reading this and you feel that you have a farm that can serve as a model for a economically viable small farm, please share your experience in the comments!