In just about every romance novel, the heroine is kept guessing about what secrets lie behind her tall, dark stranger's piercing eyes -- until she falls madly in love with him. You can create your own sense of mystique without resorting to an eye patch, creepy mansion in the hills or other romance novel tactics. Just keep her guessing a little.
Send a cryptic note telling her how much you like her. Say all the sweet things you'd never have the guts to tell her in person. Then don't sign it. Send a few more notes like that, and she'll be dying of curiosity. Even better -- send one bouquet of roses to her house every day for a week and don't sign the card.
Another cute idea is to lead her on a scavenger hunt. Set up various clues in different places around town for her to find. You could head to iTunes, download songs she loves and burn them onto a CD for her to find, or have a plate of the cookies you baked for her waiting at a neighborhood bakery. The final clue should let her know once and for all how you feel about her.