The moviedb module provides the tools to maintain a large database, and is set up for a Movie Database however it can be modified for any type of relational data (ie, Band - Album/Book - Author, etc).
The module treats movies, people (actors, directors...) and companies as separate nodes. This allows a great flexibility and extensibility.
Update 16 August 2011
Apologies for lack of maintainance, I'm going to try to actively work out the issues with the D6 version. As always, your patches and suggestions are very much appreciated.
I'm also going to start work on a D7 version. If anyone has any time to help with this, it would be greatly appreciated.
There are known bugs in the script, which are outlined below. Please do not post issues about these bugs (unless you are posting a patch).
Example Roadmap
6.x-dev release
Integration with Views
Add new fields through control panel (still very buggy, but works and have little control over them after creation)
Actor and Character Functioning, but produces error messages that don't effect end result
Bug fixes (and removal of unneccessary features)
Metadata import
Bulk import? Probably not, as I think other modules might be able to do this?)
See issue #381684: Future Features
3. Documentation