When I was in fourth grade we found a black cat on the playground the day before Halloween! The principal let us keep it as a classroom pet (can't see that happening today!) and we named it Pumpkin (we got to vote on the name and the only other one I remember was Boo, which I voted for).
We've had three other black cats at home: Kashka, Mickey (named after the mouse, of course), and Ethel Anna ("Annie").
What about Krishna (means black in Sanskrit), Nigel (derived from the Latin Niger, which means black), Shyamalan (the famous director known for spooky movies). Let's see...Lucky would be cute, too (since it's bad luck if a black cat crosses your path), Sweep (for chimney sweep, usually covered in soot), Cinders, Olive (black olive), or Eclipse.