I just discovered that virt-top is now in Debian.
virt-top (which I wrote) is the far superior alternative to “xentop”. I wrote it after having to manage some servers with only xentop available. I wrote it because xentop was so crap.
Why is virt-top better? It supports more statistics. It works with libvirt so it works with almost every hypervisor not just Xen. It has a much nicer UI and documentation. And it has advanced logging modes so you can leave it running in the background and capture information for your website/database/stats/monitoring.