David Parker - www.hellodavid.com
or www.baylinartists.com
provides keynote presentations to middle school and high school students. He can tailor the engagement to your school's needs (like if there is a particular theme). He's toured nationally and has a slew of references.
Just because you live in NY and the speaker is in CA - check their website - sometimes you can piggyback an event if they are speaking in your area and save $$$.
The middle school kids at our school really got into the assembly to learn how to Stack Cups. It's called speed stacking or something like that. It was very popular and the kids talked about it for a long time! I know they have a website but I can't remember the name. Search speed stacking and you'll find it.