Happy Valentine's Day everyone. Here in Japan, things work a little differently than where I grew up (the U.S.). Generally, females give chocolate to males on Valentine's Day. And then a month from now, March 14, males return the favor on White Day. Check out Kids Web Japan for more on Valentine's Day and White Day and the role confectionary companies in Japan had on their growth (one reason why I'm positive Halloween will continue to grow in popularity in Japan over the coming years).
Our favorite simple Valentine's Day song is Skidamarink (or Skinnamarink, if you prefer). There are many great recorded versions out there (you can find a free online version at Songs in Sign). If you wanted to look for one to download at iTunes, I would recommend the version by Sharon, Lois, & Bram, or the Wiggleworms Love You version.
For more simple Valentine song ideas, check out CanTeach.
Happy Valentine's Day!
Update: If you prefer your Sninnamarink with a bit more of an edge to it, try this version by Green Day (sort of).