Pennies are useful to throw at "spangers" --those able-bodied, dreadlocked, pierced and tattooed high school/college-aged kids that sit in front of the McDonalds (with a help-wanted sign in the window) on the 16th Street Mall in Denver or the mall in Boulder and beg "Hey dude, ya' got any spare change man?"
"spangers" = spare change (rs)
And let's not forget how useful they are, when thrown out your car window by the handful into the street, as you are passing a long line of homeless guys... ;0)