Visually? Some very cool ones are Victorian Englans, especially Victorian Horror (mmm, Victorian Age Vampire and Rippers...). Long dark mist alleyways, coats, canes and hats. From Hell would have to be a visual zenith for it.
Visually I've always loved anything to do with Samurai, from Kurosawa's triumphs with The Seven Samurai and Ran, to one of my absolute favourite anime ever made, Ruroni Kenshin. The elegant designs of their armour, kimono, and swords, contrasted with the violence of a swordfight. Kenshin in particular just took it up to a stylised extreme, making the fights beautiful too, until their aftermaths, especially with the two OVAs.
Of any recent Sci-Fi, I don't think anything has visually captured me like Firefly did. It's the freaking anti-Trek! Rverything's dirty, second-hand (at best), rough and ready and works as a result of constant mainetenance and prayer. The fusion of Wild West and Space made for something fantastic.