Ah, looking further, it meets all of your technology requirements. It does have multiple privilege levels, but they're not particularly fine-grained. There's a project in the works to fix this.

The API looks pretty simple -- I hacked together a quicklinks module in about half an hour.

It's a little biased towards creating a community site, rather than a corporate site, but with the default configuration, it might be a strong base for what you're trying to do.

The notion of "taxonomy" looks quite powerful, but I've not got my head round it fully yet.

The photo album software is a bit poor. There was a hacked-on module for gallery, but the drupal people have decided to replace it. They're not feature-for-feature yet, unfortunately.

Oh, and it's a doddle to install.