A really tight hug and the assurance that you didn't forget the day, it's just that.... life came in the way :S

You should cook for her. Regardless of whether it turns out good or not, I'm sure she'll appreciate the effort.

Try the suggestions given byArthur, Chrisdf and Sarah. They would really work! Happy anniversary, anyway!

If I were you, I would wrap her in my arms, give your best puppy-eyed look and genuinely say to her, "Happy Birthday darling" and seal it with the best kiss you can muster. Hopefully, this will mend things up. Best excuse to rekindle a relationship. @Seda, Arwa: Simply love your retorts! You both crack me up!

You have broke up with her so, just a greeting card will do.