What is XCP
XCP is the open source version of XenServer, which is a Citrix commercial product. It's of course based on the Xen hypervisor. XCP is written mainly in the OCaml language, with some parts also written in Python and C. It is a very mature product, which works easily, and is fairly easy to install.
If you don't have the requirement to have EC2 compatibility, and that you are searching for something easy, then it's the option of choice.
How to install it?
XCP is available in Debian starting with SID / Wheezy (eg, it's not in Squeeze). If you have Recommends: activated, then simply do "apt-get install xcp-xapi" to get it installed, then read the /usr/share/doc/xcp-xapi/README.Debian.gz to know how to use it.