This year we framed our bean seeds in a "greenhouse" made from green construction paper. The plastic sandwich bag is stapled inside and the student names are easy to read on the "roof."
Dr. Jean offers a great list of discovery bottles:http://www.drjean.org/html/monthly_act/act_2002/12_2002a_css.html
Apples after 7 days. One slice was clean when put in the jar. The other was handled by everyone's dirty hands as we came in from the playground.