I got a book called "Charcuterie: The Craft of Salting, Smoking, and Curing" which has several different sausage recipes of different types as well as other things like how to make corned beef, pastrami, cure hams etc. Every sausage recipe I've made from this book has been great and it has good info on how to get started.
I've been getting casings from sausagemaker.com - there may be other/better places, I just haven't looked around that much. They have a "home pack" of casings, which is short parts of casings with sizes that aren't really uniform but just fine if you're making your own sausage - the price is better for these.
If you really want to get deep, there's a book called "Meat Smoking and Smokehouse Design" which has sausage recipes and a lot of great plans for different types of smokehouses - my idea of a good read!