As sung by the elves in Rivendell. It's an iambic tetrameter hymn, and one of the longest texts in sindarin.
The hymn A Elbereth Gilthoniel is perhaps one of the most iconic texts in sindarin. It was published in the Lord of the Rings, and has since been subject of extensive debate and analysis. Tolkien fortunately provided a loose translation, and have in various publications (most recently PE17) explained the hymn in detail. It is certainly beautiful and very elvish.