WebGUI for Virtualization?

Are there any virtualizations that can be accessed via a WebGUI too? I mean the administration part is enough on a terminal, but we need a virtualization/webgui solution for "customers". So that they could for ex.: reboot their guest machine or reach it when it's "frozen" [bsod/kernel panic] or maybe clone it, etc. There is Xen with the xen-shell, but it's not good because it's only available via terminal. Any solutions?