Well, then you may just have some flower arranging vases waiting to be converted! I must attribute this notion to my Mom (happy belated mother's day, everyone!) who gave me the bright idea.
The one pictured above is a little bit large, but smaller ones are perfect. Use them to keep away funk in the classroom, then when they are done wash them out (thoroughly!) and -tada!- brand new vases.
This one is currently in my (house) bathroom. My rosebush is going crazy right now. Not bad, eh?