Awesome works by Packard Jennings. The one that cracks me up the most is described as following on his site:
"This small, sixteen-page pamphlet is produced to put inside the postage-paid, business-reply envelopes that come with junk mail offers. Every envelope collected is stuffed with the pamphlet and mailed back to its original company."
More work can be found on his site, including a series of proposed "fallen Rapper" PEZ dispensers and plenty of DIY downloadable fun at.
Previously on Boing Boing:
• Tis the season to STICK IT TO THE MAN