An easy way to make cards is just with construction paper and markers! You can be as fancy or simple as you like. Throw in some patterned paper, punches, glitter, stickers, buttons, etc...the possibilities are endless! Or you could also just print off some valentines from any of these great sites....
Family Fun Everything Valentine's
My favorite thing to do is make hearts out of things! Brownies, cookies, jello, sandwiches, pancakes and rice krispies are all fun things to cut hearts out of. These are all simple and fairly inexpensive things to make and just by cutting a heart shape out of them you get a special treat for a special person!
Do you have any other creative ideas? I would love to hear about them!