Today is Valentine's Day. I'm sure you've thought of this idea many times, but this is a reminder. Concert tickets. Theater tickets. Grungy local band at the local pub tickets. Your local philharmonic, music festival, jazz nightclub.... Something in the future, something adventurous. There's nothing more romantic than future plans and live performances IMO.
You can just go online, find something you like--months from now even. They do not have to be the very best seats in the house (just try not to sit under a balcony) Far back is fine. The side is fine. At the San Francisco Opera House, I saw one of my favorite ballet performances ever from a seat in the very last row of the very top balcony. If you're lucky enough to live in LA, the cheap seats behind the orchestra at Disney Hall are great, as Joshua Redman proved.
Print the tix out, tuck them into a card if you have one, but even if you don't...just fold them like a card and draw a heart on it. If you really want to ice it, also go online and reserve a hotel room near the venue.
Who wants to go out on Valentine's Day anyway?