My favorite Valentine ever is the card Ralph got on the Simpsons that made him fall in love with Lisa. I see a lot of my "kid' self in sweet little Ralph. I know his rejection and bottom dwelling-nerd status well.
I found artist Brandon Birds "Law and Order" cards brilliant. http://www.brandonbird.com/svutines.html
We can't forget http://www.someecards.com/ . This site is THE go to for any occasion cards.
And finally (because i am already sick of Valentines Day) a bunch of random cards. Remember, the person you love is 72.8% water.