I'm wondering what everyone uses (if anything) to keep on eye thier older servers disk drives. Along with regular backups what software can help protect servers by alerting you to hardware degradation before its too late?

Haven't heard of anything like that. I believe most hosts just monitor the ports and when the hard drive fries, they just replace it ASAP.

Here ya go (if you're on linux): http://smartmontools.sourceforge.net/

Works very well.

For Windows http://www.passmark.com/products/diskcheckup.htm