Upside-down on he back of a jeep: "If you can read this, help me flip this over."
"Tax Self Righteousness"
"Clinton for President" with a picture of george Clinton
"Re-elect Bartlett"
"Re-elect Gore"
"I love my Country but fear my Government" (Used to have this on my truck. Everyone liked it because it can mean almost anything.)
"Truth is, there's always a bigger fish."
"My other car is a piece of Sh*t too."
<img src="http://www.playdreaming.com/images/carclub.jpg">
"An eye for an eye just makes the whole world blind. -Gandhi"
"Part of the Problem"
<a href="http://www.dribbleglass.com/Jokes/bumperstickers.htm">Dribbleglass</a> has a ton more.