I did that a couple of years ago ...for my mum and dad. Booked them a table at a Chinese restaurant - all expenses paid including the cab there and back.
They were in shock.
Maybe it's something you could do for a couple you really care about - for a close friend or a family member. You'd have to kinda find out what they've got planned for Valentine's without giving your surprise away (just to make sure they're both free on that day).
Depending on your budget, you could book them a hotel (too) or maybe a weekend away.
***VALENTINE'S FIND OF THE DAY***
