Sun xVM VirtualBox: Open source virtualization application
In case your Windows requirements are not much then you can go for Sun xVM VirtualBox which was taken over by Sun and offers better support. The good thing about VirtualBox is it runs on a number of host platforms as compared to other virtualization platform. It offers high performance virtual machines for its guests.
It offers support for both GUI and rich CLI commands and you get a faster and seamless experience with mouse pointer integration, seamless windows, time synchronization, shared folders and dynamically adjustable screen resolution.
It provides better hardware and device support with VESA Virtual Display Adaptor, Full ACPI, multiscreen resolutions and NIC supporting NAT. It offers security in terms of zero data leakage between virtual machine and military specification architecture. It's free for personal use and you can download it here.