Find an organization that will do letter exchanges between students in Spanish and English. Get your students to choose a person to write to and encourage them to tell the pen pal a little about themselves and ask questions of the potential pen pal so they can write back in English, helping both students learn a language. Describe how letters should be written and how you should address the different sexes in Spanish also, depending on whether they are friends or it is a more formal relationship.
Work through a business letter in Spanish on the whiteboard, discussing the grammar, phrasing and formal words that need to be used. Then ask the students to complete a short quiz on the contents of the letter, answering in Spanish.
Discuss a vacation the students may have had in Spain or make one up. Describe where you stayed, the food you ate and the entertainment you saw while you were there. Ask the students to write a thank-you letter incorporating all this to their hosts.
Go over the story of "Romeo and Juliet" briefly. Ask the students how they would write a love letter in Spanish, depending whether they are Romeo or Juliet. Using "Romeo and Juliet" takes away some of the discomfiture some students may feel about doing this exercise, as they are only acting.