And the winner is...
There were 190 correct entries (once I'd removed all duplicates!). I asked my daughter to pick a number between 1 and 190, and she said 142. The 142nd entry was Motxam, so congratulations, get in touch by email (firstname.lastname@example.org) and I'll arrange for your voucher to be sent to you.
The correct answer was the SI-DAN - M08 Tactical Vest - Iron Black, at http://www.firestartoys.com/Shop/Minifigure-Parts/SI~DAN-Body-Wear/8255-SI~DAN-~-M08-Tactical-Vest-~-Iron-Black.html
We'll be holding another competition in a week or so, this time sponsored by LEGO, the prize for which is so cool I don't want to give it away!