Through the years I've played hundreds of games, but only a few have made me play them over and over and over.  Or in the case of MMO's, resub and resub and resub.  These are games that are so good to me that I just can't stop playing them, whether its because of friends, or an online feature, or its just so good!  It will be games spanning numerous platforms.

Here is my list:

StarCraft 1

 Played for atleast 7 years, well worth the initial 50 dollars I spent on the battle chest (lol remember those?). 

Legend of Zelda: Link's awakening

My first Zelda game, played it over and over, got the sword that shoots lightning, all 3 orcarina songs... so endless.  So worth the 25 dollars.

Final Fantasy XI

My First MMO, initially played it for 4 years, then kept quitting and resubbing ever since.... must...resist.....resub

Sonic and Knuckles

Too fun for words, spent at least 3 years playing it.  Heck I still play it on emulators.  Never actually bought it, always played at a friends house or a daycare center when I was extremely young, or dl'd it haha.

StarCraft 2

SC1's predessecor, and I still play it!  60 dollars?  That's it?!  With the amount of time I've played it for?!

MarioKart 64

I just got lightning, and I'm going to wait until you are flying over a gap to use it ;)  Never actually bought this game either...

Those are my games that I couldn't stop playing when I was younger, or am playing now.  If you put any of them in front of me, I could still play them and be entertained. 

What are yours?

Some of the Sid Meier Civilization games, maybe a couple of the Total War games, DAOC way back when, Mario Kart DS, Duke Nukem 3D, and a bunch of adventure games like The Neverhood are always good for a quick play through a couple years down the road. I'm sure I'm forgetting some.

When I was younger my answer would have been very different. A Link to the Past, Super Mario RPG, CS 1.6 (especially this one - I put so many hours into this game it is unreal).

Warcraft III - mostly user-made maps enthusiast

Final Fantasy XI - oh boy, this game was my first mmo and really got my neurons totally have a party but sometimes there is always one crashing it haha

WoW - same feeling as ffxi in the start. played vanilla a long time, pvping most of the time, burning crusade i barely played, the other ones i raided and now i am completely fed up with these kind of games.

WoW pretty much destroyed potential long years in gaming, because now everyone wants to be like Blizzard.

Hoping GW2 or Archeage will give me new steam.

Final Fantasy XI.

God there is so much quiet love for that game. See it mentioned more and more lately (as with many of the older MMOs). :)

It was my one true MMO love. I'm fighting the urge to go and buy FFXIV even though I know it's just FFXI's ugly sister. I know they're improving it but I know it's going to be a terrible experience. Still.. my hope that it will become FFXI v2 makes me want to play it now.

I'm hopeless.

VGA-Planets: One of the best, if not simply the best turn based strategy game ever.

The Mechcommander series: Brilliant RTS. The community produced an insane amount of campaigns and missions.

The Diablo series. I am not too happy about D3's RMT, but each to his/her own.

I am still playing the first 2.

The civilization series, not sure you can count that since it's a series but I've played them forever. And Alpha Centuri.

For an mmo, Guild Wars. I played WoW for a number of years as well.

FFXi.. i always resub at random points just to see whats going on in the world. the game was the first mmo that made me warm on the inside.

Diablo 2 with the new mods.

thats about all i can think of that are online. the rest are classic ps1 and 2 games.

my list would include;

secret of mana series

secret of evermore

Lufia series

final fantasy series - apart from the ones that came after 10-1

street fighter series

zelda series

and there are probably a few more i can't recall at the moment because i just play too much games in general :P

super mario bros.

super mario bros. 3

tetris

betrayal at krondor

civilization 2

Originally posted by Tirinas

my list would include;

secret of mana series

secret of evermore

Lufia series

final fantasy series

street fighter series

zelda series

and there are probably a few more i can't recall at the moment because i just play too much games in general :P

breath of fire series, arc the lad, suikoden. this is an awesome list though.

Eve Online, still playing it, definitely the winner for longest time spent playing for me

Played each of the Homeworld series several times

The God of War, Devil May Cry and Super Mario series; even though those aren't individual games I still keep playing games in those sets so I have spent years of time playing them, and I intend to continue doing so.

Counterstrike Source. I don't know what it is about that one, but it's friggin addicting!

Longest play for me would be old console ROMs on emulators.

There's an ancient one (mid-80s) called Elevator Action that I still enjoy.  Totally 8-bit with pixelized graphics in a side scroller environment.  I'd get all buzzed up bar hopping then stop at the all-nighter arcade and shove quarters into the game.

Now I just load it up on PC. :-)

1. FFXI hands down, first mmo ever played and I enjoyed every second of it. Now i compare games too ffxi. not that its supirior to all games but it holds alot of fun things and memories to me. havent played another mmo that did that for me, not even wow which i played at the same time. Also noticed others played XI for yrs and mentioned it also, its great to see others like/remember/play this game like i did. :D

2.WoW, i played it, enjoyed it, then moved on >.>, just wasnt as memorable to me as ffxi was... but i still put time into it. still dont know why.

3. Mana series also, always pull out the legend of mana every year and start over.

4.Resident evil series, good horror survival i tend to enjoy and find myself playing over and over again

5.Disgaea series, meh why not? luv the characters and the comedy with the over exagerated scenes and moves :P

Wurm Online.

Super Dodge Ball.

Tecmo Bowl.

Final Fantasy VI or better known as III.

Road Rash

MLB The Show.

FFXI  , 5 years playing it (stoping some months here and there)

stoped like 1 year ago aprox. then they upped the max lvl , played it to 78ish and bleh ><

FFXI as other posters have mentioned, I'd go back to it tomorrow if i hadnt had to take a 2 years out due to personal reasons, to far behind to play catch-up.

FFXI about 5 years

They just dont make quality MMO's like that anymore.

Only WoW and LoTRO

EVE is the game I keep going back to.  The depth and adrehenaline rushes are as good as it gets, and well worth any annoying things you have to deal with. 

Homeworld series, old turn based fallout games, and the Fire Emblem games, and Dragon Age 1 are things I keep going back to for single player.  And Soul Caliber in all forms.

Warcraft III - Played for many many years, both playing custom maps and even developing my own maps.

EverQuest II - Played since 2005 and quit and came back many times. Such a great game (before the latest xpacs and f2p)