One Day by David Nicholls

One Day follows best friends Emma and Dexter over a 20 year period as they stumble through their 20's and 30's.  The story only enters their lives one day a year, July 15th.  Their witty banter to the longing and the tension between the two of them makes you love this pair.  However, sometimes the decisions and the paths they take leave you frustrated (as only an outsider looking in can be).  From the back of the book, Tony Parsons describes it as, "the best weird love story since The Time Traveler's Wife" and I can only agree.  This story gets in your head and stays there.  It has really left an impression on me.