The tradition at my high school is to allow students to audition to give the graduation speech, rather than to allow the numerous valedictorian’s to give one. In the past students have rapped and done other creative things. What would you like to see/hear/receive from your graduation speech?
If I were given this opportunity, I would aim for a speech that is remarkably eloquent, erudite, and inspiring. I’d include some humor and emotion throughout the speech whenever appropriate. It would leave the audience a lasting impression.
If I had to audition, I would turn my speech into spoken word poetry. I love poetry and typically my performances go well, plus I think it has the same effects that @GMKoon mentioned which I also feel are important.
It’s your graduation. Chances are you’ll never see most of these people again. Unless you have an amazingly moving ‘normal’ speech planned, go with something fun and weird. A speech made entirely of puns, cliches, or jokes would be my choice to listen to. Have fun and just go with whatever you’re good at and like.