In return for eternal servitude and recruiting new Bacchae, Bacchus gives Orpheus a magic lyre. With it, Orpheus becomes the most famous musical act in all of Greece. As he becomes more and more obsessed with fame and glory, though, he also becomes very possessive of the lyre. He even tries to go back and rescue it when Bacchus's Cavern is set ablaze.
Similar, but not identical, to Hercules's Lyre.
Although the lyre looks like it's made out of gold, bronze, or some other sort of metal, it is actually made out of wood. (When the lyre is caught in the fire in 1.21 - Lyre, Liar, Iolaus calls it "firewood" instead of saying that it would melt in the fire.)