When you’re building a website, the content management system is key. If you get a good one, you’ll have to do very little custom coding, and custom coding is what makes websites expensive. I strongly recommend you choose one that has widespread adoption, you don’t really want to be a guinea pig, if the agency upsets you/folds/f*cks off, then you can be left with an expensive, non working site. Do not go with a system that is owned by one agency, go with a standard.

There are hundreds of options, from commercial systems like Opentext & Microsoft CMS, to open source like Drupal, Wordpress & Joomla. I would recommend an open source solution that has widespread adoption. With open source you don’t get left in the shit when the vendor changes their product, business model, gets bought, or goes bust. (I learnt this the hard way, years ago we invested loads of time into Macromedia’s Spectra. Then they dropped it) . Open source also means no licence or cpu fee’s.

A good way of testing adoption is to go to elance.com and search for the technology. At the moment, sharepoint yields 700 developers, Drupal 1,300 and Joomla 3,500. For you that means you can find a developer to take the site on for $10 - $20 an hour, way cheaper than an agency. If you fall out, you can find another developer easily.

In the open source CMS market Drupal, Wordpress & Joomla are the most popular - check out the links below - you get a lot of plugins like job boards, discussion, real time chat, FAQ’s, surveys etc. Many high profile sites use Drupal (e.g.: MTV UK, BBC, the Onion, Nasa, Greenpeace UK, Kleercut ) so I’d probably go with that if I was building a community site. For our site at Projectfusion.com we use Wordpress, as it’s a simple site, and wordpress is super easy to use and setup.

Links

http://www.cmsreview.com/ - reviews of current CMS systems

http://askville.amazon.com/pros-cons-Joomla-Drupal/AnswerViewer.do?requestId=6833886 - old review of Drupal and Joomla