Don't think that Valentine's Day is the only day out of 365 that a romantically inclined card or love note is appropriate. Surprise your girlfriend on any with a love note, because not only will this romantic gesture tug at her heartstrings better than a Taylor Swift pop song, but regularly writing and giving love notes will remind you both of how much you love each other. In fact, in a series of six studies researchers at the Massachusetts Institute of Technology conducted and published in the "Journal of Personality and Social Psychology," found that regularly communicating "I love you" increased a couple's happiness and feelings of love.

Sappy Sticky Notes

Who says a love note has to be in an expensive greeting card? Step out of the card store and head over to an office supply store for a pack of sticky notes. Write short, one-sentence descriptions about things you love about your girlfriend, or cheerful reminders about what makes her the most awesome girl you've ever met. Then, stick them wherever you want. For example, you could write "You're so beautiful," and post it on her bathroom mirror for her to see when she wakes up.

Post Office Paramours

Everyone loves getting mail. Your girlfriend is no exception. Instead of handing her a love note when you're on a date, put your note in a fancy envelope and mail it to her from the post office. Add to the suspense and surprise by not putting your name on the card's envelope so she has no idea what it is until she opens the envelope. For an extra romantic touch, choose an envelope that's in her favorite color.

Hidden Hearts

Scribble a thoughtful quote, a favorite memory or other sweet things that make your girlfriend smile. Then, hide the note in secret, unexpected places. She'll find them when you're not with her, and they'll cheer her up and keep you in her thoughts. Example places to hide a love note include under her pillow or in her makeup box.

Mailed Memories

The next time you and your girlfriend go on a trip together, buy a postcard from the city or town that you're traveling in. Write down some of your favorite memories of the trip together, and give it to her a few months later. This keeps the memory of your time together alive in both of your minds.

Puzzle Pick-Me-Up

Write a love letter on a sheet of paper, glue it to a piece of cardboard, and then cut it into pieces. You now have an instant love note puzzle. When she puts all the pieces together, she can read your heartfelt thoughts. Place all of the pieces in a box and give it to your girlfriend as a gift, or give her one piece at a time over the course of several days or weeks to build the suspense.