Anyone interested in game worlds beyond games? I mean, have you tried to dig up more information about game's world after finishing the game?
For example I like books set in the world of the Sanctuary (Diablo). And I totally love "A pocked guide to the Empire", beautifully written book about Tamriel (The Elder Scrolls). It was included in Oblivion (Collector's edition only I guess). Does anybody know it?
There would be more of it but I try to keep the first post short.

I'm definitely interested in that sort of thing.
Heck, I'm even in the middle of coming up with my own original world for my own games, and trying to refine it with even more details and whatnot. The problem is that it's pretty vast (set on various planets over a very wide span of time, stretching from before the creation of this universe to after its destruction), and trying to make everything seem distinct and believable is going to take a while. (For instance, each sentient race generally has its own language, and sentients from distant worlds often find themselves having to find a means to communicate with each other. There's no aliens-from-lightyears-away-suddenly-speaking-English-like-it-was-their-native-tongue here!)

I sometimes look up this stuff even if I'm not interested in the game, I have too much time on my hands.

Hey, is there a thread without your post in it? You're everywhere. And here I thought I have plenty of free time :) Anyway, great performance.

Yeah, I pretty much get booted from every community for have the most number of posts, whether they're on topic or not.

The 36 Lessons of Vivec (from Morrowind) is the greatest bit of prose ever to appear in a videogame.

I've always enjoyed the warhammer and 40k universes. Also Forgotten Realms is well developed and there have been a number of PC games set there.

Heck yeah, I love that stuff! Morrowind to me is the best TES game out.. Of course that's biased because I only played Morrowind and Oblivion but.. you get the picture, it's SEVERELY better than Oblivion, yo.

Agreement.
TES game lore is rather good for a read. While it is all up online in various places , it was more fun in Morrowind walking about and coming across new topics now & again.
There are two editions of the 'pocket guide' the first coming with an earlier game. Things can change quite a bit over time.

As a huge fan of KotOR, I have looked up quite a bit of additional information about that era of Star Wars, but mostly through Wikipedia or Wookieepedia articles, not through actual source material, like the novels, comics or the pen n' paper RPG.

To be honest, I pretty much ignore all the books in Morrowind, but I accidentally read one of the 36 Lessons and it just blew my mind and forced me to read them all. It's definitely something else. I think it's the only game lore that's ever made me deeply, deeply jealous.
Oh, and I'm not sure if this counts, but in Metal Gear Solid 2, one of the random Arsenal Gear conversations has the Colonel giving a blurb (or pitch?) for a comedic dystopian sci-fi story. It's a great moment in a sequence full of great moments, but it stood out because of how ridiculously detailed it was.

Like a lot of people stated here, I love The Elder Scrolls universe.
I spent days reading books and other things about it in the UESP wiki and everywhere else I could find. Damn, I even printed some of the best books of Morrowind, like Mystery of Talara and some of the Vivec's lessons.
I've never been this much influenced by a game :)

The Neverhood had a huge wall covered in text telling the story of it's universe. It was really long and sort of like the bible. I read every bit of it in game. Not sure how long it took, but it was a time consumer.

A few more lore-heavy titles, probably already mentioned :)
- The Elder Scrolls: Morrowind and Oblivion (I haven't really played Daggerfall or Arena much, largely because I can't find them anywhere. Maybe GOG can solve this someday :) )
- Fallout 1 and 2 - We all know this one. If you don't. Go buy it. Now. It's only six dollars, after all.
- Blizzard games - all of em have decent backstories, though often not entirely in-game.
- Warhammer and Warhammer 40,000: Dawn of War is the most popular game here, but as a tabletop wargame, there are huge amounts available on both worlds out there both online and as published books. I play Warhammer Online right now, and the amount of lore available is just insane.
- Forgotten Realms (D&D): FR is the most popular D&D setting, and has had more games based on it than any other. (There were actually a couple Eberron games, namely DDO, but it didn't get that popular.)
- Basically everything that's come out of Bioware since Baldur's Gate. A lot of these fall under Forgotten Realms, but Bioware is famous for adding tons of information to it's games, specifically through dialogue options. They also did the Kotor games, which are probably the best Star Wars games out there. They also did Mass Effect just last year.
- Civilization: An odd addition, but it does have quite a lot of 'backstory' even if it is actual historical fact :)
- Age of Empires: Similar to Civilization, it does actually contain a lot of real information used as backstory in the game.

FYI Arena is freely available from the elder scrolls website. :)