It's gotten to the point where one 2'x2'x7' bookshelf won't hold all of my roleplaying books and boxes. There has been a general infestation of science fiction in my American History and I think the fantasy horror tomes have given my education bookshelf a growing case of Lovecraft and King. On top of this (soon that will be literal) my new Ebay RPG lot purchase will arrive next week. Let's not even go into board and card games.
While I don't have an easy physical answer for the moment (and perhaps I don't really need one), I do have a virtual one: librarything.com. This is a cool website for cataloging, organizing, reviewing, and sharing texts of all sort, including (of course) roleplaying games. Nearly every roleplaying book I've checked is in their database, though my personal collection doesn't get overly obscure. It's also another way to meet like-minded people and compare libraries. Librarything gives you the option to sign up and write book reviews in return for free books. The website also offers library word clouds and a multitude of ways to look at your collection. If you have a really large collection, you can buy a cheap scanner and scan all your books in.
You can log your first 200 books free, but it must remain public. To go private and exceed 200 there is a small monthly, or one time payment fee where you name the price. You can see my personal library, warts and all, here.