Now I've seen it all
The new Bagel Virus takes the cake. (Update: Also known as Beagle, Bagle, etc.)
It comes as an EXE attachment (which would be blocked by all current versions of Outlook and Outlook Express) with the subject "Test" and the message body "Test, yep."
It doesn't even attempt to socially engineer the user into opening the attachment (no celebrity photos, no fake Microsoft security patches, etc) and yet the distribution is listed as "High."