How to identify disk abusing process?

[Bob - BLU]

So here is a Linux question that's been nagging at me.  Is there a simple (command line) way of identifying processes that are creating heavy disk i/o?  I suppose I could wrap some shell script around sar, or poke around in /proc, but thought asking here might be more productive and fun.  Any thoughts?

A secondary, less important, question is how to identify the file(s) being accessed.