Food

• A written invitation at a time and place where he would least expect is one way to creatively add a charming element to your invite. That said, a note passed in history class probably won't do. Instead, try ordering a pizza and having the cook write out "Prom ?" with some olives. He will be in a good mood, since you are already treating him to a food he loves, thus half of your work will be done.
  
  

Radio

• Just about every pop radio station has a good chunk of programming where people can call in to request and dedicate songs. Call at a time when you are sure your boyfriend is listening, (this may take some suave convincing if he is not a regular listener) and request a song that holds significance for the both of you, and mention to the DJ that you are hoping he will go to prom with you.
  
  

Notes

• Another creative way to put your invitation in writing would be to leave a note in his locker, car, or pretty much any place he goes everyday and is guaranteed to see it. A handwritten note would technically work, since the creative, charming part is his surprise upon discovering it, but consider upping the creativity. For example, place the note in his favorite CD case or magazine.
  
  

Public Address

• This is a common method used by men proposing to their girlfriends, but it can also work for you and your boyfriend. You need not shell out money you don't have for an expensive announcement at a pro sports event, as the resources you need to pull this off are already at your disposal. For example, ask the announcer at your school's football or basketball game to insert the invite into his regular announcements or a break in his play-by-play duties.