You could make a card with a classic mix tape of love songs on it. No credit unfortunately, but I know the cassette tape was made out of an old pair of jeans. A good alternative to over-the-top girly cards.
This fun card by the long thread is extra awesome because your valentine receives a multi-coloured crayon in the shape of a heart. What more could you want!
I love a good play on words so this card from Lark and Lola caught my eye. They even sent a Starbucks gift card on the back.