The most common Valentine's Day poem is the classic "roses are red, violets are blue, sugar is sweet and so are you." A less cliche poem would be "This is for you on your special day, you opened up my heart and showed me the way. I love you to bits, more than words can say. To the love of my life, happy Valentine's Day."
Another sweet yet short poem for a significant other would be "my dear Valentine, if the sun refused to shine, and romance ran out of rhyme, still then even you would have my heart until the end of time." If the significant other enjoys silly poems, a poem to use would be "Valentine's Day is filled with love, poems, chocolate and roses, funny pictures and silly poses. Hearts and big eyes, silly cards and crying eyes, people kissing, but a Valentine as good as you is what they are missing." A funny poem to send could go something like "Violets are blue, roses are red, thought this would be longer, that's what she said." Another humorous poem to get a date laughing would be "Shiny metal and straight, narrow lines, if you were a Transformer, you would be Optimus fine."
Beyond the almost nursery rhyme poem, a classic poem like Elizabeth Barrett Browning's "Sonnet 43" from "Sonnets from the Portuguese," is short and romantic, perfect for Valentine's Day. The poem opens, "How do I love thee? Let me count the ways. / I love thee to the depth and breadth and height / My soul can reach," and is best suited for a serious romance.
For a more modern twist to send your crush, try Langston Hughes' "Harlem Sweeties," which describes in detail the beauty of a flirtatious girl in Harlem, with phrases like, "glow of the quince" and "honey-brown dream."
For Valentine's Day cynics, "Another Valentine" by Wendy Cope talks about the feeling of obligation on the holiday, "Today we are obliged to be romantic / And think of yet another valentine," though by the end romantic feelings are evident even among critics.
Other poems perfect for wooing a longtime love or an infatuation include "The Passionate Shepherd to His Love" by Christopher Marlowe, "A Glimpse" by Walt Whitman and "I Wanna Be Yours" by John Cooper Clarke.