What is the best way to cut through beef and pork bone?

I'm looking to upgrade my kitchen. In particular, I'm looking to make more roasts and stews, courtesy of a new slow cooker. Due to this, I need to know how to cut a bone-in pork shoulder "down to size", so it would fit. At the same time, I'd like to know (for future reference) what the best tools for cutting through beef bone is, just in case. I like to buy large cuts, and make them smaller, to save for future meals, as it is invariably cheaper to do so. I'm looking for a relatively inexpensive tool, but primarily I want something guaranteed to get the job done.