The church I pass on the way to my parents house had a lot of really, really good ones. I especially loved the one they had during the last Superbowl:
GOD HAS NO FAVORITES,
BUT OUR SIGN GUY DOES
GO GIANTS!
And yeah, they're not "pull-over-to-laugh-uproarishly" funny but they're often quite clever and amusing. Almost makes me start wanting to go to church again. Almost.
EDIT: I forgot, I actually took a blurry pic of it while driving back home...