Here's my bet on the October surprise.

[Speck Tater]

The FBI will round up a couple of suspicious people of middle eastern decent, possibly even connected in some way with some terrorist organization. They will "discover" all kinds of "evidence" that these people were about to set off a 10 kiloton nuke in downtown Denver, and thus "prove" what a great job Bush is doing at catching terrorists.

Of course the "evidence" will be phoney as a three dollar bill, and the "nuclear material" will turn out be a bottle of glow-in-the-dark paint from the local craft shop. But of course that won't be "discovered" until long after the election.