[magobaol]

Hi Mathias,
I think you should give a look at DevonThink.
It is a really powerful personal information database.
You can import file inside it or simply index them (leaving them in their own finder folder structure); you can make links between file and tag them, if you want. It also has an auto classify feature that helps you to categorize or move your documents based on their contents.
It has a lot of features and, even if the UI is not really gorgeous, it definitely worths a try. It is a bit expensive, but It comes in 3 or 4 versions, so maybe your preferred version doesn't cost too much.
I haven't yet started to use it at 100%, basically because I need to study my archive structure very well before start, but in this moment I'm very busy in implementing and studying other aspects of GTD, so for the moment I use it for taking my journal and for saving reference that I may meed in the future ("to be archived", despite of what Allen says...)

Regards,
Francesco