I feel like I missed alot since I didn't read the manga. So I'm reading it currently and I can say I love it more than the anime! Some facts listed below. (Might be spoilers below if you have not seen or read Black butler)
For example Lizzy is shown as a weakling in the anime as to the manga she is actually strong and took fencing lessons with her mother. She even saved Ciel, for crying outloud! Also she wears low heel shows, since she is taller than Ciel. (Chapter 57) Yes I ship them together
Another rumor, I've heard since I'm not exactly caught up in the manga.. Ciel didn't die and turn into a demon, unlike the anime. Also that the shinigami were once human.
Those who commit suicide become "Grim reapers" as punishment. They work until the day they are forgiven, a captive audience to the deaths of man. Have to bear witness to their earthly regrets and lust for life day in and day out. -Sascha in Chapter 109
Sebastian is named after Ciel dog, which is probably why Sebastian loves cats and hates dogs. That's why Kuroshitsuji is one hell of a Manga!