John Howard - Virtual Server, Virtual PC: John Howard, IT Pro Evangelist, Microsoft UK, keeps a blog on many interesting topic, especially MS virtual computing products.  Recent samples:  how to share a vm desktop with VMRC with 2 or more simultaneous remote sessions; and how to use WMIC (Windows Management Interface Commands) to generate html pages with Windows system info.  9:04:11 PM    

Sysprepping a virtual machine: Details on use of the Windows Server sysprep command when cloning virtual machines.  3:54:35 PM    

Howto for UML: Steps for installation and use of the mature User Mode Linux platform. For new development, see FAUmachine: "We are working on an Open Source Virtual Machine which started out as a User Mode Linux, and which we therefore used to call UMLinux. Since the project has evolved from a User Mode Linux to a Virtual Machine we have chosen to give it the more appropriate name FAUmachine... FAUmachine development is supported by the European Community."  3:49:57 PM    

Linux-VServer: "the vserver project: It allows you to run linux inside linux: Any distributions inside any distributions. Each virtual server has its own packages, its own services, its own users and is confined to using some IP numbers only and some area(s) of the file system. You can think of them as virtual machines."  All vms are linux, and they share the host kernel.   So there is essentially no CPU overhead.  VM disks can be resized, and vms moved easily, just like other vm solutions, getting many vm advantages with almost no overhead costs.  Active development.  3:48:14 PM