I own a slow cooker. This is a tremendously useful device that has been around for decades. Many books have been written on application after application of casseroles, stews, braises, and so on. After all, it's a big piece of equipment, so you want to get your shelf-space worth out of it. For me, although I'll occasionally branch out into other dishes, I find that it earns its keep by doing just two things for me: stock and boston butt.
The thing I like about making both stock and pork butt in the slow cooker is that it requires no thought at all. None. No consultation of recipes, no worries about how it's going to come out. Okay, I lied: I do have to think about if I'm going to be around in 8-12 hours to decant the thing. But that's usually accomplished by setting it to cook 2-4 hours before I go to bed. Ta-dah!
Stock. Okay, let's say I want to make a chicken or turkey stock. What do I do? I take a whole chicken, or a chicken carcas, or some of a turkey carcas, or turkey necks, some chicken wings and thighs, and I dump them into the stock pot. If I have some vegetables, I'll cut them up into big pieces and put them in, too. Then I'll 3/4 or so fill the slow cooker with water and cook on low for 8-12 hours. When I'm done I decant the liquid into plastic containers, put into the cooler with some ice and other freezy-things until it's cold, and refrigerate or freeze. No recipes, no ratios, nothing. If there's a trick, it's not to try to squish too many solid things into the pot.
Pork Butt. Take a Boston Butt. Put it into the slow cooker, fat side down (or trim the fat, if you're ambitious). Pour in two beers. Some sort of Ale is probably best, but whatever. Nothing too dark. Liberally salt the top of the pork. Cook for 10-12 hours on low. If you want, turn the thing after 2-4 hours. Once it's done, it should fall apart when you barely poke it with a fork.
Both of these dishes freeze nicely and are great things to have around when you need to add a little something to some dish that you don't want to spend a lot of effort on. No matter what, the stock you make here is better than anything you'll buy at a megamart and probably at least as good as what you'll get from a specialty store. And the pork has saved me on man a what-am-I-going-to-have-for-dinner night. Both are cheap as dirt. Both are dead simple.
So, if you have a slow cooker, break it out, fill it up, and let time, low heat, and liquid work its magic on inexpensive, collagen-filled ingredients. And if you're considering getting a slow cooker, don't think you need a recipe book to make it a worthwhile purchase. Sure, it's great to branch out and do more with it, but it's hardly necessary. Load it up and go, and prepare to be amazed.