Your answer to this will depend on your taste. It will also depend to some extent on your native language, since poetry is hard to translate properly and so we will nearly always prefer poems in our own language.
Of poems written in English, you can find some famous examples here:
Personally I wouldn't have chosen any of the top 9 from this list, though they are great poems. My favourite of all love poems is The Good Morrow, by John Donne (9 on the list). It looks quite dry at first, but try reading it two or three times and try it aloud - it's got more real feeling than almost any other poem.
I also love Shakespeare's Sonnet 29 (33 on the list) more than the famous 'Shall I compare thee to a summer's day', which is really just about appearances.
Finally, Elizabeth Barrett Browning's 'How do I love thee' (11) is one of the best love poems ever, often read aloud at weddings.