Making your own peanut butter is a great way to get as much as you want without additives (unless you want them!). Luckily, you don't need a roaster; a wok or deep frying pan will do, as Alton Brown shows us in his most recent video.
Alton explains that using a wok (or a deep frying pan if you don't have a wok) will give you an even richer, nuttier flavour than you would get if you tried to roast the peanuts in your oven. You'll need the wok and a food processor (you could probably pulse a blender for this if you don't have one) and some shelled, unsalted peanuts. The video walks you through the recipe and shows you what the process looks like.
Recipe aside, the real beauty here is that you can make your own peanut butter at home with little other than the peanuts and a wok. Best of all, making it yourself lets you flavour it up the way you like -- a little chocolate in your peanut butter perhaps, or, as Alton suggests, some chile oil would bring a lot of flavour to a really simple food that we probably pay too much for at the grocery store.
Wok Fried Peanut Butter [Alton Brown (YouTube)]