I've been tempted to get an autodialer (or build one) and repeatedly call back those companies who have machines calling me.
From what I've heard, the DNC list isn't all that well enforced.
We have a company who keeps calling us to sell us children's books. We have purchased from them in the past and have cancelled. They still call us with offers. Next time they call, I'll be telling them my kid is dead.
Speaking of pissing off unwanted callers:
http://classicalgasemissions.blogspot.com/2007/10/trick-or-treat-youve-won-vacation.html
...I can't believe that's almost a year old already!