The Alexander Sarcophagus at the Archaeological Museum. I took a lot of photos of it but was unable to do it justice (no tripod, no flash, and low light). Wikipedia has an entry here, although their photos aren't much better - but at least they have some description. It's a stunningly beautiful piece of work, definitely one of my favourite things from the entire trip. This is a panorama shot constructed (poorly) from several photos to give some idea of one side of the sarcophagus.