Here is a video that could be used to introduce a class about St Valentine's Day:
One thing I like about it is that it uses lots of song lyrics in the sentences the character is trying to write and it could be a good idea to make some competition in class to try to identify (and sing!!) some of them. Students could also try to "help" the man to write his love letter or valentine without watching the end of the story.
If you need more materials about St Valentine's Day, Larry Ferlazzo's blog could be of use. Here you will find more links to what he considers the best sites to learn about St Valentine's Day.
Now here is a song which is not mentioned in the video above but which is directly linked to its theme. It could represent the reaction of the lady who receives the letter from the man in the video.
The song is "Love letters", a classic, in the voice of Alison Moyet (the first version I heard although not necessarily the best, that is up to you).
To help you write valentines, here is a suggestion I have taken from Times Online. The two first lines are the "cliché" of valentine "poetry". The rest is a highly political statement and the basis for the joke.
It makes reference to an interview in which the Prime Minister, Gordon Brown, opens his heart about private matters in front of the cameras. This has been perceived by some people (the cartoonist Peter Brookes , for example) as a change of attitude in the prospect for votes in the next election.