Have you taken a look at Movable Type, I know its one of the most popular CMS software packages. There's been some controversy over its license lately, but I think its still free for noncommercial uses. It can handle multiple users, authors and stuff.
Also, reading over your post I can't help but think slashcode may work for you, the software that follows slashdot.org. Another possibility is scoop, from kuro5hin although I havent had a chance to play with it at all. So my final word: Slashcode
Link:
http://www.slashcode.com