We are using Munin to get graphs of our servers. (such as CPU load, I/O, available disk space, etc. ) Munin gives us last 24h, last 7 days, last month and last year.
The good thing with Munin is that it supports all kinds of clients, such as Windows, Linux and switches because it can monitor over SNMP.
However, we have a problem with the Munin client for Windows. Since we upgraded to Windows Server 2008 R2 it won't show graphs for some performance counters.
What options are there out there? Both free and commercial.