Virtualization Platforms of Interest:
- Proxmox VE - bare metal virtualization - open source - Hit the streets earlier this year; one update released mid-summer. Still in beta. Open source product, ie, no license fees. Concurrently runs OpenVZ (linux kernel level partitioning) and KVM hardware-abstraction-virualization on the same host. Apparently KVM for SMP windows guests is not remotely production ready; this is the 'main show stopper' here currently. Otherwise, a very slick offering with a nice web-based management interface. Even facilitates painless setup of 'clusters of virtualization boxes' and permits through-the-wire migration of VM's between nodes. Not quite 'live migration' due to footprint involved, but still very nice. And you can't argue with the price.
- OpenVZ - Linux containers - Has been around for years, a very solid product that continues to evolve. Excellent way to partition a linux host and offer virtual linux hosts with minimal overheads on resources. Free version of the derived (more feature rich) commercial offering, Parallels Virtuozzo Containers (or whatever variant name they are calling it today? :-) In theory, many folks feel that Virtuozzo for Windows is "THE" way to do virtualized I/O intensive stuff (ie, MS platform Databases, if you really must do this kind of thing). I've seen some folks debate that they still prefer Xen-style-hypervisors though, so I suppose dogma should not be the guiding principle in choice of virtualization platform :-)
- Virtual Iron - A few years out, they are still going and offer a very nice product. Xen hypervisor at the core; their secret is in the sauce (aka the management) plus a very attractive price model (linear cost-per-socket, gives you all features - including live migration, livePower, etc) - ie, no gouge-o-rama-factor for the nice stuff. Their entirely-free offering is 'a bit of a lame duck' (restrictive features, really intended for learning about virtualization) and quite different from the non-free product due to the management and installation evolution of the product in the past ~year.
- VMware - can't not mention them, but really it isn't necessary. Great product but the licensing is what will kill you. Why pay for hardware when you can pay for software licenses instead ?! Would you like iSCSI with that? Live Migration? Centralized Management? Sure, we can do it all and we'll be happy to give you a quote! :-)