How about bets denominated in bitcoins, since a lot of Website:Lesswrong.com readers don't have easy access to the regular financial system or long-distance travel capability?
Right now Bitcoin isn't a regular enough currency for the denomination of goods. It's more of a store of value.
I'm not sure if anyone has been following the appeal...
but I'm willing to bet up to several hundred dollars at even odds that Amanda Knox will be released on appeal.