Does anyone know of a good tool to test Schema.org (http://schema.org/) markup?
The Google Rich Snippet tool does not support it properly. Even with the correct markup given, it says "Insufficient data to generate the preview."
update: Now the Google Rich Snippet tool supports some schema.org markups.
This one came to my attention recently. linter.structured-data.org
I like that it generates a preview when the Google Rich Snippet tool reports "Insufficient data to generate the preview." The structured-data tool also generates a more structured, almost graphical result, which makes the results a bit easier to understand.