I already have some on my car that make people laugh but the newest ones are:

Saluki Taxi

No, my windows aren't dirty, its my Saluki's nose art!

Some of my favorites are:

Minds are like parachutes, they only work when open.

Don't blame me, I didn't vote for him.

Well behaved women rarely made history.

If you pick up a starving dog and make him prosperous, he will not bite you; that is the main difference between a dog and man.
-Mark Twain-