Boxed Ice’s monitoring service offers a awesome easy way to trace server performance and stability.
There are many tools to check your server’s availability, so Server Density is not a standard tool that just tells you “hey, your server is offline” – it’s a small script running on the server that reports the server’s health status every minute. So what you get is a detailed list of performance parameters (every singe process running, memory usage, apache information, …) for every snapshot it takes.
Server Density is available as a payed service – but they also offer a free version with less parameters recorded (and “only” for one month).
I’m using Server Density to monitor one of my servers but planning to implement it on some others too. It’s a perfect tool to analyze high load situations. You just click on the according time in the graph and you get the whole list of collected data for this snapshot.
P.s.: No, I don’t get anything for this – I really like this service and because we used it over a long period of time for free it’s just fair to help them gain some popularity.