Australia 1858 RR Half Sovereign PCGS VG Grade
Rarity of rarities. The 1858 dies were re-punched in order to extend their working life. One die was re-punched incorrectly, thus the RR error half sovereign came into being.
Andrew Crellin of Sterling & Currency has more on the subject: http://tinyurl.com/RRhalfsov
I believe the count is now at nine for the number of examples in existence.
You can verify the certificate of this coin by clicking on the following link (opens in new tab):