This tool can be used to view differences in org-mode files.
It applies an alignment algorithm that's tweaked for org-mode documents.
Its output isn't strictly a diff at all (if you want to get that, you should just use diff!) It looks okay in diff-mode in emacs.
This is how I use it! I keep my .org files in a local git repository. Before commiting a day of work, I do something like this to produce diffs.
for file in `git diff --name-only *.org`;
do
git show master:$file > /tmp/old-$file;
org-mode-diff --old /tmp/old-$file --new $file > /tmp/$file.diff;
echo "/tmp/$file.diff";
done