An easy one would be Wordpress. A more elaborate option could be Drupal or similar ones such as Xoops etc.
I personally have used xoops, mambo php platinum, envolution and of course postnuke. One thing you want to keep in mind is how secure the CMS is...sinec postnuke and phpnuke are constantly having to patch in order to fix security issues...that is why I have gone to xoops and mambo recently. They are pretty secure.
I used mambo before and actually using it on the site in my sig. It is too cubersome to implement a news site with. I went with drupal as it seems very fast, secure and has everything i need
It depends on the complexity of your news site. Wordpress is good as a blogging tool that is converted into CMS, and posting news and such should be adequately covered by Wordpress. However, if you're looking for other add-ons like user registration, forums, etc, Wordpress wouldn't be able to handle that well. I've been using NEPHP from www.nelogic.com and it's been awesome. There's also ArticleLive and Evo-Articles from www.evo-dev.com