My current personal external Getting Things Done (GTD) brain/tool is Nirvana. I recently decided to move some of my "content" related items in my Someday/Maybe list to external list options in tools that are native for that type of content.
For books I moved them to an Amazon Book Want To Read List. This is using Amazon's Wishlist option.
For movies and TV shows, I am using the Watchlist feature in IMDB.
One of the benefits of this approach was it got each of these content types into a more "non-text" list in Nirvana with more visuals, and it helped to speed up my review of my Someday/Maybe items during my GTD Weekly Review.
I also have a Wishlist on Amazon for physical things I might want to purchase. When something new comes a long that looks interesting, but I don't know for sure that it will be useful, I put them in this list. And then I review it every month or so to see if any items are really something I need. Not just something I wanted at the spur of the moment.
If you have any suggestions on other types of list tools for content, then please let me know.