search for: usedspace

I have a CentOS 5.2 box that every few months runs out of drivespace on its root filesystem. Last time I manually searched and deleted some big files, but don't remember what they were or what wrote to them. The applications I'm aware of on the box don't write to /. Is there a way to find the files that get written to the most, or grow the most over time? Doing a df gives me a