In the last few years I have collected a large amount of ebooks, papers, articles, movies, pictures, etc. (all digital).
I am at a point where I would like to organize these items into a cohesive, searchable and maintainable system. I have looked at various methods (e.g. Niklas Luhmanns "Zettelkasten", Zotero, Org-Mode) and I am not satisfied yet. Any tips?
If your data is variegated in format and form, don't look for a single tool/method solution to organize them. There is no single all-purpose organization method.
Don't start with figuring out a method to organize your information. You will end up overengineering your org method.
Instead, organize your information per "use-case". Start with a specific use-case/project (e.g. writing a blog or paper), and work backwards to figure out how to organize your data to meet the requirements of that project. Do a couple of iterations. After a couple of projects, and you will naturally discover your own data use patterns.
If you go with a super organization system on day 1, it will likely be too general and require too much effort (tagging, keywords, hierarchies, version controlled, branches, etc.) you will end up expending resources on metadata management on data that you may never ever need to retrieve and very soon you will abandon the effort.
My PKM system is very simple: a single unorganized Google Docs for quick thoughts and ideas (just bullet points), separate Google Docs files for specific projects, etc. and Dropbox for files. It's simple, searchable, and multi-device.
I also occasionally use some specialized tools like Jabref (BibTeX) for specific types of data like references, but I hardly ever write papers anymore, so these have fallen by the wayside.
I've tried wikis but due to their multipage nature, they segment knowledge too finely (often there are wiki pages hidden in deep in the link hierarchy that I forgot existed). Wikis don't fit the PKM use case that well, so these too have fallen by the wayside for me.
For me, PKMs need to in some way feel like a single broadsheet where I can easily see and touch my information without having to drill-down hierarchies and follow too many links.
p.s. I've heard good things about Evernote. It's a little too heavy for me, but many people seem to find it useful.