S.B.
You know, the one mother's day gift my mom still keeps on her bookshelf was one I did when I was probably about 4 years old -
Take a styrofoam cup and let the kids decorate it w/ markers, paint, glue thingies, whatever, then put that artificial flower/moss stuff in it, make a flower out of construction paper and a straw & glue a picture of the kid's face to it, and on the back side put Happy Mother's day, and then stick the straw in the cup. I even think it has some cutesy saying the teacher wrote on it, too - like "Bloom where you're planted" or something.
It's simple and cheap and I swear, it is still my mom's favorite.