If you've settled on Iridium, it seems to me that to achieve uber-geekdom you'd go for Ir-192 (perhaps with a lead inner lining?).
You can use it to check the welds in your X-prize entry.
You can use it to zap any nascent cancer found in friends, family, or even strangers.
On cold Winter evenings you can cuddle up together with your HP calculators and debate the probability that it's turning onto Osmium or Platinum (and how much has already decayed)
The possibilities are simply endless.