Instead of paper valentines, buy some flower seeds at the dollar store (usually 6-10/$1) and give them to your friends with a note that says something like - "MY LOVE FOR YOU GROWS AND GROWS!"
This is a good idea! I'll add it to my list of gift ideas. Why not do them up for end of year teacher gifts! It would be a nice little thank you gift to show your appreciation plus the teachers would get to enjoy the flowers.