The Dreaded Salary Question

When you're asked for your current pay, or maybe your desired pay, and i think both recruiters and companies ask for this, you suggest not giving this as a base line number. How do you decline to provide that information? What words do you use such that it doesn't shut the conversation off? So i call it the dreaded salary question. It's phrased something like this: Where are you right now in terms of salary? And what would you like if you come on board with us? What would you hope to make?