I spent a little time today researching tool alternatives to Altova XMLSpy for generating sample XML from XSD definitions.
The Eclipse XML/XSD editor provides the ability to generate XML - but it appears to have some limitations - it only generates an example for the first element it finds in the file.
Here are few other resources:
oXygen XML Editor
WMHelp.com - XMLPad
XML Schema Definition Tool (Xsd.exe)
XML in .NET Generating XML Documents from XML Schemas