Go to the nearest bookstore (if there are any in existence anymore) and go to the 'journals' section and find yourself a nice blank paged book. Spare no expense. Find one that looks and feels right for you. Black leather bound? Perfect!
Now, everyday, every other day, or at least once a week, write down in this book your thoughts about her or him. It can be a quick "I love [insert name here] to pieces!" or a poem. Some days, when the inspiration comes to you, you might feel like writing for ten minutes about your relationship and your lives together or what your life would be like without the other (hint: empty). No matter what you jot down, do this for an entire year, or until the book is full, without your lover knowing about it. Make sure to state the date at the top or bottom of every entry to provide proof of a long-term commitment to this project.
Then, when the moment or occasion feels right, on their birthday or your anniversary perhaps, casually leave the book out for them to "discover" as if you absently-minded left it out in the open. Let them read it. What happens next should be magical!
WARNING!!! This long-term project, while very thoughtful and powerful can backfire on you and can also serve as another litmus test to the status of your relationship. For example, if and when you casually leave this diary to be read and she picks it up, reads a few pages, and hands it back to you and says: "Here, I think this belongs to you." to which you reply, "But, did you read it?" and she returns coolly, "Yeah...it was sweet..." before exiting the room, (feel that sting?) that is pretty much a good indicator your relationship is on the outs. Actually, this warning pretty much applies to any romantic gesture...the reactions to any gesture don't have to be over-the-top and result in amazing marathon lovemaking each time...but disinterest like this is fatal (see Tip# 26: Acknowledgement for more on this).