I just made my first list and it is comprised of very long games including fallout 3, dragon age and mass effect and at this point contains only games I have played. It is by no means complete and I would like some suggestions from the community. The games must be both exceptionally long (preferably over 40 hours) and be single player experiences only (so no world of warcraft or modern warfare).
 
Edit - Online games now accepted! 
Also, a witty summary sentence for some of the games on the list would be appreciated, especially as I have never played some of the suggestions.

Mass Effect 2

Sims 1 or 3.
Oblivion
 
For me i just got into Civlization IV, clocked in 50 hours so far, and i haven't even won a game yet on the "Nobel" difficulty. It has a steep learning curve but it's easily one of the deepest games i have ever played. I have always been hesitant to try a Civ game since i heard how deep the games are, but buying Civ IV was one of the best purchases i made.

Pokémon. Especially HeartGold/SoulSilver.
 
16 Badges is no joke. No. Joke.

Any Pokemon game for me. Shit takes up my LIFE and I haven't even beaten all the gym leaders. I got to about 80 hours in one of them before even making the Elite 4 and have since put in 120 hours total.
 
And Animal Crossing. I actually think that it's good there's no time total on there because I'd probably kill myself

Yeah, any Pokemon game, CoD, WoW, Starcraft 1 or 2, Guitar Hero, Rock Band...

any of the square rpgs would fit this, I think most pople would say either Final Fantasy 6 or Chrono Trigger

" @Fullmetal216:  Well that's an obvious oversight on my part, thanks. "

SF4. Broke 500 hours and it would have gotten bigger if it weren't for Super's release.

pokemon

At about 16 games so far, fuck it I'll open the flood gates... MMO's welcome.

" SF4. Broke 500 hours and it would have gotten bigger if it weren't for Super's release. "

Runescape

Counter strike source because it took like two years of my life ten hours a day and I want those years back. I stopped playing online after that, lots of hostile ppl there and I couldn't stand it.

 
Mass effect 2, honestly how much minerals do I really need? Holy shit.  
 
FFXIII, because boss battles are so difficult when you don't use a walkthrough and you will die like alot of times, they you think the best solution is just grinding. Took me 60 hours to finish, 30 extra hours of grinding that could of been used more wisely.  
 

Persona games... pretty much any of them. 

Disgaea series.

Added a bunch of suggestions, also threw in peggle.

" Any Pokemon game for me. Shit takes up my LIFE and I haven't even beaten all the gym leaders. I got to about 80 hours in one of them before even making the Elite 4 and have since put in 120 hours total.  And Animal Crossing. I actually think that it's good there's no time total on there because I'd probably kill myself "

Well that's 20 games in the list, only 70 more to go! Fuck.

If your not too good at GTA IV it might take over 40 hours to finish...

Harvest Moon, Civilization, Total War, Diablo, X-COM

The lack of Tetris is disturbing.

Monster Hunter Tri (It's shorter than the PSP version but still well over 100 hours..)
 
World of Warcraft 
 
Resonance of Fate (70 hours in, almost near the end BUT there's a fairly lengthy optional dungeon afterwards)
 
Demon's Souls
 
Diablo 2
 
Etrian Odyssey II
 
Street Fighter 4 (Those short plays add up. I got over 70 hours on it. And I rarely play online)
 
Any games that occur in the Shin Megami Tensei universe (And there's a whole lot of franchises in here)

Some great new suggestions keep them coming. Out of interest how many of you have looked at the list itself?

All of the Total War games.

World of Warcraft needs to be on your list for sure, unless your not counting mmos :P People have literally died because of that games super addictive nature and immense time investment requirement.

I need more suggestions, the list itself is here if you want a look.
http://www.giantbomb.com/profile/walkertr77/games-that-will-eat-your-life-away/46-30825/

Borderlands, you CAN play it by yourself and it'll be fine.

Monster Hunter Tri
 
Oh man can it...

TF2, Fallout 3 and WoW. I spend a lot of time with all of those games. And I had like over 100 hours with the first L4D.

I played at least one hour of Animal Crossing: Wild World every day for over a year.

SimCity, any of them. For me, SimCity 4 completely soaked up literally weeks of my life.

"

Counter strike source because it took like two years of my life ten hours a day and I want those years back. I stopped playing online after that, lots of hostile ppl there and I couldn't stand it.

Final Fantasy 13, Persona 3: FES,  and Persona 4 make up my life draining games.

The Disgea franchise. My play time in Disgaea 3 is now 260 hours or so and I play it often o.O

Persona 3 clocked me in at 76 hours....and I tried to rush through the game.
 
Oh and Morrowind.

pretty much any Civilization type game will destroy your life.

Only 40+ Hours?
Well Pokemon of course, I'm almost 100+ Hours in and I'm not even close to catching em' all! :D
Online Wise, Little Big Planet (Making levels, costumes,) Finding levels
Socom 2 Onlien wise
Final Fantasy XII (Specifically)
Persona 3 & 4
Tekken 6 is my main fighter and the one I'm best at, prob got over 80+ hours in that easily. 
Xenosaga 3
Digimon World 3
Gran Turismo 4
White Knight Chronicles (Around 30 Hours for story, over 40+ for online)

Vagrant Story- about 30% of the game is unlocked after beating the final boss.  Nevermind how many hours it takes to reach the Grandmaster Breaker rank.
 
Monster Rancher- I played a painful amount of this game back on the original playstation.  I think you can technically "beat" this game, but that doesn't mean you stop playing.  Plus, you get to make monsters using your CDs!

Right amended for the new suggestions, only need about 60 more...

WoW is multiplayer? News to me. 
 
JRPGs, they are long. Especially stuff like Disgaea where if you plan to do all the optional stuff you could actually be looking at a lifetime of gaming.

I put 190 hours into SMT: Persona 3 FES and 125 into SW: KOTOR.   I don't want to even think about World of Warcraft.  It actually did suck the life from me.