In the last year I sold off all of my Star Wars Saga Edition rulebooks, and then followed up by selling off what was left of the WOTC 3.0/3.5 books and my Pathfinder books. It could be assumed that the reason I divested myself of these books is because I "broke up" with those systems and didn't want to have our prom pictures around anymore.
Unfortunately, that isn't quite the deal. It's a bit more practical than that. I've got a small house, with a diminishing amount of space, and if I wanted to explore other game systems, I needed to actually have room in my allocated gaming space. That led to some hard decisions, mainly, to get rid of stuff that took up a lot of room that I wasn't playing at the time.
I'm not actually a pack rat, in general, but if I had my preference, I'd have a physical copy of every RPG with which I ever ran an enjoyable campaign. Broken rules, hard feelings, edition changes, or setting meltdowns aside, the fond memories would likely be enough to keep a lot of them in my possession.
Of course, in this day and age, a company that has PDFs of their material is my friend. All of that Pathfinder stuff I divested myself of? I still have the PDFs of all of those books (hence why I'm still playing in a Pathfinder RPG game).
Why is the above paragraph relevant? Well, if WOTC and Lucasfilm had managed to put out PDFs of all of the Star Wars Saga books, I would likely have purchased them. I was slowly starting to pick up 2nd edition PDFs of WOTC's D&D material, before WOTC determined that the best way to fight piracy was to eliminate the only legal way to purchase PDFs.
I was idly thinking about what I would have in my ultimate library of RPGs if I had the space and the money to rebuild my collection of games. This is more or less what I came up with:
Dungeons and Dragons
Basic Set, Expert Set, Rules Cyclopedia
Advanced Dungeons and Dragons 1e
All of my old hardcovers, the FR boxed sets, the Greyhawk boxed sets, and the FR sourcebooks
Advanced Dungeons and Dragons 2e
The "second run" of the hardcovers, including the Players Option stuff. Most of the FR sourcebooks and boxed sets, some of the DragonLance stuff, the Spelljammer boxed sets, Greyhawk boxed sets and sourcebooks, Dark Sun boxed sets and sourcebooks, Ravenloft (oh my yes) boxed sets and sourcebooks, and probably at least a few Planescape products.
I could do completely without the PHBR series, as I don't remember having that many fond memories of any of the kits or spells or stuff from those. The DMGR series had some fun titles, and the HR series would be a must for this hypothetical collection.
Also, anything that was produced under the Lankhmar license. I love Fafhrd and Grey Mouser, and man did I screw over some of my friends playing a wizard in a Lankhmar campaign. Good times.
Marvel Super Heroes
Basic Set, Expert Set, The Fantastic Four and Avengers sourcebooks, and the one cosmic adventure series that was the first published series of adventures that my friends and I tackled as written.
The 2nd Edition Boxed Set (that was the one with the black background with Superman and Batman on it, right?), the Batman sourcebook for same.
The RPG boxed set, Knight Hawks, and Zebulon's Guide to Frontier space.
Top Secret S.I.
The boxed set. Maybe the one equipment guide, from which our agents purchased a Yugo back in the day.
The original boxed set. I never looked into the Ghostbusters, International stuff that came out.
Pretty much the whole line. This is one I never got past the character creation process with, and yet for some reason its one that haunts me still. Probably because Star Drive and Dark Matter were both neat settings.
Dungeons and Dragons 3.X
The whole she-bang. Well, I was never much for Eberron (not a knock, just wasn't a priority for me to get into it). The softcover "X and X" books for 3.0 never did much for me, and much of that saw a revival in the 3.5 material, so I suppose I could do without all of that.
3rd Party d20
Most of Green Ronin's stuff, Ravenloft (again), and maybe the DragonLance stuff from MWP for old time's sake.
Star Wars (WEG)
Pretty much the whole she-bang.
Star Wars (D20)
Again, most of the stuff that came out. The rules weren't always as intuitive as they could have been for a Star Wars game, but lots of neat toys for a RPG campaign.
Star Wars Saga
Again, even though the last few books had some broken and/or really incomplete rules, I'd still have the whole lot in my collection.
I'm sure I've left off some stuff from the above list, and I don't know that I'll ever have the time, money, and space to get all of my little friends back under one roof and into a warm, loving, kind gamer home. However, there are a few games I played that I could care less if I ever have a copy in my gaming library:
Middle Earth Role Playing
It could have been the GM, but we went on an epic journey to the remote corners of Middle Earth only to encounter some spellcaster of some kind that cast a spell on us which required us to look through 3788 pages of charts (okay, maybe not that many) just to figure out what he actually did.
Then it took us almost as long to figure out what effect swinging a sword in his close proximity actually did.
Not enough of a positive for me to care to revisit the setting.
I'd have all of the old FASA Battletech boxed sets in my (non-RPG) gaming library in a split second, but Mechwarrior, despite some interesting concepts, didn't do much for me.
"So we stat out our mechanics and support staff as well as our Mechwarriors?"
"But we just stat them out so that we have their stats if we really need them, because if everything goes the right way, we're just playing our Mechwarriors?"
"And most of the times we're playing them in the Mechs."
"So the only stats that matter 90% of the time are gunnery and piloting. This whole thing is to provide a little more backstory for when we whip out the maps and play battle tech, except you are going to make us jump through hoops before we have a shot at getting an Atlas or something cool."
A Last Word
Before I go, I should probably clarify. I don't have Call of Cthulhu, Mutants and Masterminds, Savage Worlds, or the 40K RPGs on the list because I am running/have recently run them (except for CoC), and I actually have the physical books in my gaming library at the moment.