I've got a spreadsheet which reads a few tables I've set which tracks CPU usage (for now).

I haven't got it set to read disc I/O or anything else at the moment, but it gives me a rough idea of the cause of the slowdown.

It's shows the last 12 hours, by day/hour, by hour and by day.

It also tracks current running queries and any of those queries which don't conform to our best-practice documents.

It's a bit basic but it works for me.