WIthout a lot more specific information on what you want, my first guesses would be:
Drupal, then
XOOPS, or
Joomla!. Depending on your needs and your resources, you can probably find a way to get a workable solution from one or more of these.
These are full blown CMS (Content Management System) setups with everything you need to build a nice, clean web presentation with Content Management, indexing, etc. It sounds to me like you're looking for web site design first, then content managment, then maybe some data handling. I'm not sure how much capacity you need or how much "geek factor" you're willing to invest, and those will both have a significant impact on your choices.
-PatP