<p>Which industry-class database has the most <strong>unique</strong> features? (with "unique" meaning that no other RDBMS has them)</p>

<p>I think my choice here is Oracle 11g:</p>

<ol>
<li>Flashback query (you can estract data as it was a moment in the past)</li>
<li>ASM - automatic storage management</li>
<li>Native code compilation of stored procedures</li>
<li>Audit features (tracing everything, from logins to statements)</li>
</ol>

<p>and many others.</p>

http://en.wikipedia.org/wiki/Comparison_of_relational_database_management_systems
&&
http://en.wikipedia.org/wiki/Comparison_of_object-relational_database_management_systems
would be where I'd start.
As to truly "unique" features? I've seen things I thought were unique that turned out to be common once I did more digging :)