Muguet. In the "language of flowers", the lily of the valley signifies the return of happiness. Legend tells of the affection of a lily of the valley for a nightingale that did not come back to the woods until the flower bloomed in May.
Lily of the Valley is "my" flower, because I was born in May (note to other people born in May, I'm sorry, but you'll have to find another flower). I love these, and I've never tried to grow them so I don't know if they're difficult and fussy.