One that's been around for a while, but is kind of related -
"Keep Working - Millions on Welfare are Depending on You."
On one of my cars I had "Buy a Gun - Piss Off a Liberal." I also had one that went, very simply, "I (Heart) Explosives." That one would cause lots of people to start laughing like crazy up when they would pull up behind me, but after the 9/11 attacks it just wasn't funny any more, so I scraped it off.