I am always using my whiteboard/mimio/interactive board for vocal warmups! If you don't have one you could also print these out and use as posters! Here is one that is simple and fun with leaves!
Students should follow the path of the leaves with their voices. I have my students use a vowel sound so that we are warming up for singing and do not have any crazy noises.
You can have the students follow your finger, use a dry erase marker to trace the pattern, or use your interactive pen. I have included a powerpoint presentation along with a PDF of the graphics.
There are blank slides at the end for you to allow students to create their own vocal paths.
Leaf graphics were made by Math in the MIddle. Check out their other great products here: http://www.teacherspayteachers.com/Store/Math-In-The-Middle