Boxgrinder
BoxGrinder Build is an easy to use command line tool to create appliances (virtual images) from simple plaintext appliance definition files. BoxGrinder can produce appliances for a variety of virtual and cloud platforms using plugins supporting technologies such as VMware or EC2.
See the Quick Satrt page (http://boxgrinder.org/tutorials/boxgrinder-build-quick-start/) for an overview of how to use BoxGrinder.
Spice support in virt-manager
With Fedora 15, virt-manager has been updated to support Spice, the complete open source solution for interaction with virtualized desktop. It's now possible to create a virtual machine with Spice support without touching the command line, and benefiting all the Spice enhancements without hassles directly from virt-manager. Thanks to the spice-gtk library, you can also develop a client in Python or C, or with gobject-introspection bindings.