Pulled this off awhile back, not on valentines, but it worked very well...
First, I setup a "girl's day out" for my wife and her cousin. Called wife's cousin, asked her to take my wife out shopping/getting a pedicure/etc. I needed wife out of the house for a couple hours for setup.
While she was out, I went over to my parent's house, since they drink lots of bottled water, and recycle the bottles. I knew they'd have pleanty of empty bottles on hand. Also went to the store, got a dozen tulips (or maybe roses, can't remember), a nice quality bubble bath, some of those glass "pebbles" for fish bowls, some ribbon, and a pack of tea candles.
Knowing my wife likes to take relaxing baths, but she almost never treats herself to one, I setup a nice bath for her to come home to. Used the pebbles + water to fill the water bottles (after removing the labels and putting a nice piece of ribbon around the screw threads, sealing with hot glue), and get them bouyant with a flower in each bottle.
Made a nice playlist of some of her favorite relaxing music, loaded it on an mp3 player, and set that up through a battery-powered speaker. Tied back the shower curtain with some leftover ribbon, spread the tea candles around the tub, and through the rest of the bathroom. Filled tub, got it nice and bubbly, and set the floaty flower-bottles around in the water (it took a few minutes to settle after it got done filling).
Finally, lit candles, turned out lights in the bathroom, and set the book she was reading on top of a hand towel.
I think she was in that bath for about 2 hours. I could do no wrong for months afterwords.