cook her favorite meal & serve it by candle light.
draw her a nice bath with bubbles, candles, rose pedals, etc.
give her a full body rub
play some soft music & dance with her in the living room with the lights down low.
rent a movie you know she'll like & watch it with her while snuggling on the couch.
clean the house for her.
or get crazy & do a combo of all of the above!
Have the house cleaned & get the bath set up, let her soak while you finish making the romantic diner which is followed by a slow dance in the living room before you set up the movie & give her a massage as you watch it together...
long ago I was given a romantic evening...
my boyfriend (at the time) had set up a nice bath for me w/ candles, incense, bubbles... when I got out of the bath it was dark & there were paper hearts on the floor leading down the hall to the living room. Each one had a note "I love you because________" (each with a different reason) & when I got to the living room, he was standing there with his hand behind his back. He presented me with a bouquet of homemade paper flowers. Very sweet.