The Content Query WebPart (CQWP) really makes fun. If you want to aggregate or spread information within a single site collection this webpart will be your friend.
If coding the appropriate XSLT and editing the needed files is not your daily business here is a list of links that I find to be very helpful
- How to: Customize the Content Query Web Part by using Custom Properties
- SPFieldType Enumeration (Microsoft.SharePoint)
- Getting the raw XML data
(I will update this posting whenever I find new helpful links.)