Many people "hate" Valentine's Day, especially if they don't have significant others. But the original Valentine's celebrations were not celebrations of romantic love, but the love of God. And that is something ALL can celebrate - man or woman, young, old, single or married. Most likely there were more than one Saint Valentine in the early Church, but tradition holds that at least one was known for writing with love and encouragement to Christian communities. This Valentine's Day, do something to honor the original meaning of Valentine's Day: the love of God and encouragement of fellow Christians.
Make/send a Valentine to someone who wouldn't otherwise receive one - a widow(er), an unmarried family member, a neighbor.
Make many Valentines to take to a nursing home and pass them out to the residents. (This would be great to do with kids!)
Read Corinthians 1:13 (suggested by Jen):
Write a love letter to God, telling Him how much you love Him and thanking him for the loved ones in your life.
Support marriage by offering a married couple you know a night of babysitting so they can have a night to recharge. (Think especially of couples you know who don't have family in the area!)
Write a letter thanking the people in your life that have been examples of love and/or marriage. Tell them how their examples have been beacons for you.
Pray. For your spouse (or your future spouse if you are not yet married). For your loved ones. For those who are lonely on Valentine's Day. For those who don't know God's love.
If you are going on a Valentine's Day date, bring the love of God with you! Pray before, during, and after your date (suggested by Amanda).
Read about St. Valentine. Beth suggested this kids' book about St. Valentine and the true meaning of Valentine's Day. Here are a couple other options as well: Saint Valentine by Robert Sabuda and Saint Valentine by Ann Tompert.