While tempted to suggest "draw and quarter", the fairest treatment would be forcing them to pay my internet bill. After all, if they consume my bandwidth and quota without my permission, they should pay me for the usage. The fact I pay for an internet connection does not bestow permission on anyone to send me spam.

Other: hanging, drawing, and quartering comes to mind.

First hang them from the neck until NEARLY dead.
Next drag them through the city behind a horse (or car).
Then tear out their intestines out of their living bodies.
After that attach each limb to a horse (or car) and tear them off.
Display the parts across the country.

Worked wonders against enemies of the Crown.

One hour of community service (picking up litter, public land and utilities maintenance and improvements, etc) per spam email sent.

1,000,000 emails sent, mandatory 12 hour work day imposed = 228 years labor.

Sounds reasonable to me.

one hour of work shoveling garbage at a chemical waste dump per message sent is more appropriate

That works as well
Any onerous labor that serves the public at large, especially work that would otherwise be paid for with government funds, would be fit punishment for them.

I wonder if all those annoying Cirtcuit City popups on DaniWeb are considered spamming?

I have never seen them. Use a popup blocker, or I think you can just go to your CONTROL PANEL and turn them off.

in fact with very limited action you can get rid of all advertising on Daniweb

I go along with that!