Books you will LOVE:
The Ballad of Valentine by Alison Jackson
Bella at Midnight by Diane Stanley

Valentine Jokes
Love Poems
Valentine's Day
Alphabet Soup
Valentine's Day Words
Woven Valentine
A Very Unusual Valentine
 

Literature to enhance informative writing:
The Totally Terrific Valentine Party Book by Judith Bauer Stamper 
 

More Holidays
The Little Red Schoolhouse