A wiki with limited write access would work well. Limited in that only a few individuals across the organization/company would be able to update the main portal page, and then each team or sub-org could have people that maintain their section of the site. This would encourage collaboration and get involvement from more people, so they might actually care about what is on the main internal company page, rather than take what they're given and complain about it.
I worked on a medium sized system administration organization in IBM, and we used a Wiki based portal for accessing team documentation and putting together best practices. It was put into place four years ago when I was there and per a friend still there, is still used and liked across that organization. Other teams we worked with adopted similar solutions for their own use.
We deployed the original site on a Sun E450 with 2 CPUs, and about 1G memory. The site itself was running tikiwiki, which is a php based content management wiki package. These days I would look into a wiki package that is also a ticket management system, so users can open a ticket directly to fix problems with the portal. Redmine or Trac are great tools for this.
I should add that the site running on an E450 also hosted a wiki for another organization, and all told served content for grand total of about 300 users, spread across the USA. The type of hardware required is going to be dependent on the size of the organization and the amount of traffic, of course.