NiXPS on OpenXPS, Office 2007 SP2 and Windows 7 XPS Viewer.
Global Graphics now blogging on XPS, PDF and related stuff.
java-axp: 100% Java XPS file reader (old, but had dropped off my radar).
Make sure you UpdateLayout() when using XPS in WPF.
Markware blogging on preflight and data conversion
Nuance OmniPage 17 to ‘Unlock the Green Office’.