A question I am often asked! Sucanat (or rapadura) is dried, unrefined cane juice. As you can see, looking into my jar of sucant, it is granular, not crystalized.
The primary benefit to sucanat is that it is unrefined. This means that it still possesses trace minerals and is nearly in its natural form. Thus your body will metabolize it slightly slower, not causing as quite a sharp spike as white sugar does, and you will actually derive some small nutritional benefit from consuming it. It's not totally empty calories.
White sugar is cane juice that has been separated and stripped (and bleached) to pull just the concentrated sugar out. Thus it is highly concentrated and has absolutely no nutritional benefit (and many would argue quite a few harmful qualities when consumed regularly).
From what I have read on the subject, raw sugar/turbinado sugar/organic sugar/etc.--those off-white or light brown sugar crystals--are less processed than white sugar, but when all is said and done, there is not much difference between these raw sugars and white sugar. You will be better off choosing sucanat over raw sugars.
All that said, let's remember we're still talking about sugar. Sucanat is still a sugar, and sugar is sugar is sugar! Sucanat is simply sugar very near to its "whole food" form. It is a better alternative to white sugar, less stressful to our bodies, and provides a tiny amount of nutrition. However, I am not promoting the wide-spread, frequent use of sucanat. From everything I have read and continue to read, it seems wise to keep our sugar-intake (even sucanat) to a minimum on a regular basis.
In terms of sourcing sucanat, a co-op is probably your best bet, as you can typically order it in bulk. Small bags of sucanat and rapadura in the grocery stores normally cost a fortune. Through my co-op I buy organic sucanat in 15lb. increments at $2.19 per pound. Those 15lbs normally last us 6-8 months. (That's a good read on how much sugar we consume, if you're curious.)
As far as the importance of buying organic sucanat or regular sucanat, I buy organic because sugar cane is typically a heavily (pesticide) sprayed crop. However, if you can find a fair trade sucanat, that should be a good product, as fair trade products are typically grown in eco-conscious, sustainable ways.
A few baking tips:
Generally, sucanat can be added in a 1:1 ratio in place of white sugar to recipes. Some sources will recommend using slightly more sucanat, often 1 1/3cup of sucanat to replace 1 cup of sugar, because sucanat, being less refined, is a bit less sweet. I normally just sub 1:1.
You need to keep in mind that using sucanat is like using brown sugar, so if you are trying to make a white sugar cookie and you use sucanat, it will come out like a brown sugar cookie. This rarely becomes an issue for us since we don't eat a lot of desserts and there aren't a whole lot of recipes where this will really become an issue. However, if it is an issue, consider using organic sugar (or another raw sugar), as the difference between using organic sugar vs. white sugar in the final product will be minimal, while you will have still chosen a at least a slightly better option.
Sucanat works wonderfully in cakes and pies and muffins. When making cookies, you have to be a bit more careful. When you cream the butter and sugar, you really have to beat that sucanat and butter together much longer. You might notice a slight difference in texture with cookies. For us it has not been an issue, but everyone needs to find what works for them.