I'm hoping someone can shed some light regarding the current state of
virtualization on Debian. Since I like my information first-hand, i
thought I'd ask here for some real-world use cases. I am currently
gathering some data in order to redesign the network infrastructure of
the company i work for. I've been directed by some fellow sysadmins
towards ESX and ESXi, but the pricing seems a bit over the top and
honestly, i don't know if i actually need the whole thing, also
considering that i am not familiar with enterprise-grade virtualization
solutions.

Basically I'm looking for a robust system that will allow me to deploy,
host and manage virtual machines. The need for different services is
growing in my company and having virtual machines for each would be ideal.

I'm looking at a really small setup so the performance is not that big
of an issue, but I am definitively looking at reliability and
flexibility. There will probably be a main physical server running about
a dozen machines, not all of them concurrently.
Being a corporate environment, I am also concerned with data and network
security, but i don't really know where I should be looking for
information, as designing a system with no real-use knowledge of the
components can be quite a hard task.

I've worked with hosting control panels and I like the idea of being
able to manage the system through a web browser. To be more specific,
I've worked with [ISPConfig](http://www.ispconfig.org/ispconfig-3/) which has support for OpenVZ containers.

I never had to actually use that so far, but from what I saw on the
management interface it seems like it would be a pretty simple solution
and I like that. The issue is that i need to host Windows server VMs on
it and OpenVZ does not seem to be supporting it oob.

I am also currently looking at the various pages on the debian wiki on
Xen, QEMU, OpenVZ and the suggested softwares to work with
virtualization. If you have other valid sources of information, they
would be really appreciated.

EDIT:
The proposed solutions are:

1. The free vmware [ESXi](http://downloads.vmware.com/d/info/datacenter_cloud_infrastructure/vmware_vsphere_hypervisor_esxi/5_0)
2. [Proxmox VE](http://proxmox.com/products/proxmox-ve)
3. VirtualBox with [phpVirtualBox](http://code.google.com/p/phpvirtualbox/)
4. [Openstacks](http://www.openstacks.org)