You can find more details on this sale on the login screen as you're loading into FarmVille. Game cards can be purchased at most 7/11 stores or GameStop locations, and eCards can be found on the Zynga website. They even have custom eCards for Valentine's Day. This sale ends on February 14th, so hurry up and make your purchases if you want to take advantage of the bonus Farm Cash.
Check out the rest of our Valentine's Day 2011 coverage right here.