Here's a couple more:
"Prevent Inbreeding: Ban Country Music"
and,
"Asalaam malekum", which translates to "peace be with you" from Arabic, and is IMO a perfectly wonderful sentiment. A lot of people where I live are literally shocked that I would say such a thing - I guess it sounds like I'm a muslim - but at the same time, I hear "God Bless You" almost constantly in daily conversation.
Another wonderful sentiment, something I can really get behind, are the Beatitudes:
The Gospel According to Mark said:
Blessed are the poor in spirit, for theirs is the kingdom of heaven.
Blessed are they that mourn; for they shall be comforted.
Blessed are the meek, for they shall inherit the earth.
Blessed are they which do hunger and thirst after righteousness, for they shall be filled.
Blessed are the merciful; for they shall obtain mercy.
Blessed are the pure in heart; for they shall see God.
Blessed are the peacemakers: for they will be called the children of God.
Blessed are they which are persecuted for righteousness' sake: for theirs is the kingdom of heaven.
Blessed are ye when men shall revile you, and persecute you and shall say all manner of evil against you falsely, for my sake.
Those are deeply comforting words, even for someone who does not believe.
Lastly, as long as we're talking about bumper stickers, there's a site with some really interesting stuff at
UnAmerican.com.