Once the kids are asleep, take 15 or 20 minutes to share dessert or a glass of wine. It's not a night on the town, but it will be time for just the two of you to get away from the usual routine.
The Romance Brigade loves the picture frames from Crate and Barrel; think of them as an inexpensive way to surround yourself at home and the office with the faces of the ones you love.
Skip the candy and flowers -- it's too obvious that you forgot a gift -- and go for something meaningful like a nice gift bag of your significant other's favorite things, such as her favorite drink or his favorite magazines.
Surprise your S.O. with a coffee at his or her office or bring lunch. The unexpected is always appreciated.
Melt a dark-chocolate Hershey bar and buy some strawberries for quick and easy fondue.
Don't just send a cheesy e-card. Find an actual, bona fide card and put a great picture of the two of you inside, with a heartfelt message.