Planning web site content development is difficult.

I'm working on a large scale website content development project and I'm slowly realizing that my method of cobbled together site-maps and word documents isn't functioning as robustly as I'd like. We're still in the planning phases, fleshing out what content is available currently for us to use and what content we need to develop and in the process I'm getting a really mucky and unusable text document. I really wish there was software to help manage the planning and creation process run more smoothly.

I'd like to see software made for web designers that enables more flexible content strategy development. Here's some initial thoughts:

• Flexible site map development which can be connected to drafts of content broken down by pages or sectional content/modules. If the site map is restructured, content follows pages/modules associated with site map objects. Granular/modular restructuring is what I'd really like to see.
  
• Change tracking in drafts of content in a non-obtrusive way (ie. view most recent draft, view with content changes from specific collaborators, etc.)
• To dos for researching content that's needed (i.e., product selling points, supportive images and references, resources to link to from content, etc.) including the ability to assign those tasks to particular members of a team
  
• Associating drafts of content with other informational assets such as images, tabular data, forms, etc.

I'm sure there are software packages or web applications that provide this functionality out there, so leave them in the comments! I'd also love to hear about your workflow for creating content before a site is launched.