Guest VM Images
Guest Virtual Machine Images
OrionVM PV-HVM Templates
OrionVM has made available a library of guest images ready to boot on Xen 4.X+ hypervisors and pv-ops dom0. These images are compatible with the example Debian 6 dom0 in the Xen Beginners Guide.
Aurélien Jarno's Debian Images
Aurélien Jarno provides qcow2 formatted installations of Debian which can be used with Xen.
Stacklet provides a large array of PV guest images for download. Subscription is $10/month.