The first one I did I found at this website. It's a simple butterfly template that I printed on pink card stock and then cut slits into. I used crayons in the slits one year and lip gloss the other. Both were a big hit!
For the boys, I used this website. I've printed the jar template onto both blue and brown card stock and both look fine. I went to Dollar Tree and found packages of plastic bugs that I glued on using a glue gun. A little caution when buying the packages, there are a one or two in each bag that aren't bugs so you may need to buy a few more than you think.
Photo from http://www.dandee-designs.com/2012/02/love-bug-valentines.html
If you have younger students, K-2 this will be a hit! This year I have a much older class of fourth graders so I will have to come up with a new or variation of this idea. Let me know if you have any ideas!