In the past, I've put together little Valentines for people in the office, and would leave it on their desk along with a small bag of candy that I put together.
I would usually buy some bags of Dove chocolate hearts, Valentine's Hershey Kisses, gummy hearts and things like that, and then put an assortment in a small Ziploc bag, and leave them with a valentine.
Last year, I left Super Friends valentines that I found online.