With all the recent ports, remakes, re-imaginings, HD re-releases, etc., I've been wondering which games this community has bought the most times over.  For my own list, I'm going to take a somewhat liberal view of what constitutes a new version of a game and group some fighting game sequels and Mega Man versions together.  I'm excluding games I've bought extra copies of as gifts for others.  Here's a list of every game I've received or bought more than one version of.  The scary part is that some of these games have many more versions that I never had the platform for or simply skipped, so some of you may have far more versions of some of these games.

SEXY SIXES
-Street Fighter II Turbo/Collection1/Collection2/Super Turbo/Anniversary/HD Remix: SNES, PSX, PSX, GBA, PS2, PS3

FANTASTIC FIVES
-Final Fantasy IV: SNES, PSX, GBA, DS, PSP
-Street Fighter Alpha/2Gold/3/3GBA/Collection: PSX, PSX, PSX, GBA, PS2

FABULOUS FOURS
-The Legend of Zelda: Ocarina of Time: N64, NGC, NGC, 3DS
-Super Mario Bros. 3: NES, SNES, GBA, Wii
-Seiken Densetsu/Final Fantasy Adventure/Sword of Mana: GB-Square, GB-Sunsoft, GBA-JPN, GBA-USA
-Mega Man X1: SNES, GBC, PS2, PSP
-Mega Man 1: GB, PSX, PS2, PSP
-Mega Man 3: NES, GB, PSX, PS2
-Super Mario Bros.: SNES, GBC, GBA, Wii

TERRIFIC THREES
-Chrono Trigger: SNES, PSX, DS
-Final Fantasy I&II: PSX, GBA, PSP
-Final Fantasy V: SFC, PSX, GBA
-Final Fantasy VI: SNES, PSX, GBA
-Super Mario Bros. 2: SNES, GBA, Wii
-Super Mario Bros.: The Lost Levels: SNES, GBC, Wii
-Lunar: Silver Star Story/Legend/Harmony: PSX, GBA, PSP
-Mega Man 2,4,5: GB, PSX, PS2 [MM5 is included here because NES MM5 bosses appear in GB MM4]
-Mega Man X2: SNES, GBC, PS2
-Capcom Vs. SNK/Pro/2: DC, PSX, PS2
-Street Fighter IV/Super/Arcade: PS3, PS3, PS3
-Metroid/Zero Mission: NGC, GBA, GBA
-Street Fighter EX+a/2/3: PSX, PSX, PS2
-The Legend of Zelda: NES, NGC, GBA
-Street Fighter III Double Impact/Third Strike: DC, DC, PS2

TREMENDOUS TWOS
-Zelda II: The Adventure of Link: NGC, GBA
-The Legend of Zelda: A Link to the Past: SNES, GBA
-Super Mario World: SNES, GBA
-Yoshi's Island: Super Mario World 2: SNES, GBA
-The Legend of Zelda: Majora's Mask: N64, NGC
-Space Channel 5: DC, PS2
-Shenmue II: DC, XB
-Metroid Prime 1-2: NGC, Wii
-Metroid Prime 3: Wii, Wii
-Wario Land II: GB, GBC
-The Legend of Zelda: Link's Awakening: GB, GBC
-Castlevania: Symphony of the Night: PSX, PSP
-Mega Man 6: PSX, PS2
-Mega Man X3-6: PSX, PS2
-Kirby Super Star/Ultra: SNES, GBA
-Legend of Mana: PSX-JPN, PSX-USA
-Castlevania Chronicles: PSX-JPN, PSX-USA
-Donkey Kong Country: SNES, GBC
-Klonoa: PSX, Wii
-Ys I&II: DS, PSP
-Metal Gear Solid 2/Substance: PS2, XB
-Metal Gear Solid 3/Subsistence: PS2, PS2
-Metal Gear Solid/Twin Snakes: PSX, NGC
-Perfect Dark: N64, 360
-Conker's Bad Fur Day: N64, XB
-Rez/HD: PS2, 360
-Rhythm Tengoku Gold: DS-JPN, DS-USA
-Mega Man & Bass: SFC, GBA
-Samba de Amigo: DC, Wii
-Super Mario 64: N64, DS
-Super Puzzle Fighter II Turbo: PSX, PS3
-Tetris Attack/Puzzle League: SNES, DS
-The Legend of Zelda: Twilight Princess: Wii, NGC
-Animal Crossing: NGC, DS
-Final Fantasy IV: The After Years: Wii, PSP
-Mega Man 7: SNES, PS2
-Mega Man 8: PSX, PS2
-Tetris: GB, DS

Although I do not have a lot of copies of the same game, there are a LOT of games I have more than once, if you count remakes and ports. I decided to count the millions of tweaks to Street Fighter games as separate games to prevent it from becoming too complicated:

Beyond Good & Evil: GC, PS3
Castlevania - SotN: PSX, PS3
Chrono Trigger: SNES, PSX. Should really get the DS version some day.
Discworld PSX: JP and EU version
Final Fantasy 7: PSX, PS3
Final Fantasy 8: PSX, PS3
Final Fantasy 9: PSX, PS3
Final Fantasy 12: Standard & Zodiac International
God of War 2: PS2, PS3
Kingdom Hearts: Standard & Final Mix
Kingdom Hearts 2: Standard & Final Mix
Legend of Zelda - Ocarina of Time: N64, GC, 3DS
Lufia 2: SNES, DS (hey, it's a remake!)
Marvel vs. Capcom 2: DC, PS3
Mega Man: GC (MM collection), PS3
Mega Man 2: NES, PS3, GC, Genesis (Wily Wars)
Mega Man 3: PSX, PS3, GC, Genesis
Mega Man 4: PSX, GC
Mega Man 5: PSX, GC
Mega Man 6: PSX, GC
Mega Man 7: SNES, GC
Mega Man 8: PSX, GC
Mega Man 9: Wii, PS3
Mega Man X: SNES, PSP
Mega Man X3: SNES, PSX
Metal Gear Solid: PSX, GC
Metal Gear Solid 2: Standard and Substance
Onimusha: PS2, Xbox
Penny Arcade Adventures Ep.1: Xbox360, PS3
Pocket Fighter: PSX, PS2
Prince of Persia: Sands of Time: GC, PS3
Prince of Persia: Warrior Within: GC, PS3
Rayman PSX: JP and EU
Resident Evil: PSX, GC (can you really count that as the same game!?)
Resident Evil 4: GC, Wii (and PS3 soon!)
Shadow Hearts Covenant: Standard and Director's Cut
Silent Hill 2 PS2: JP standard, JP Restless Dreams, EU 2-disc edition
Sonic the Hedgehog: Genesis, GC (collection), PS3
Sonic 2: Genesis, GC, PS3, Xbox360
Sonic 3: Genesis, GC, Xbox360
Sonic & Knuckles: Genesis, GC
Sonic Adventure: DC, PS3
Street Fighter Alpha: PSX, PS2
Street Fighter Zero 2: PSX, PS2
Street Figher Zero 3: PSX, PS2
Super Mario Bros: NES, SNES, Wii
SMB2: NES, SNES, Wii
SMB3: NES, SNES, Wii
Tales of Destiny: PSX, PS2
TESIV - Oblivion: Xbox360, PS3
TMNT 2: NES, Xbox360
TMNT Turtles in Time: SNES, PS3
Tomb Raider: PSX JP and EU, Xbox360
Tomb Raider 2 PSX: JP and EU
Xenoblade: JP and EU (preordered!)

I can't recall everything I've rebought, but the game that has suckered me the most is Final Fantasy IV - I have bought it 5 times over... SNES, PS1, GBA, DS, and PSP.  Gets me every time, even after all this time.

Good news: There's help available. Talk to your doctor about Buyinex.

Four:
Ys I & II (PC Engine, Saturn, Eternal, Complete. Also the I-V compilation disc that came as a bonus with some other game. Not counting that, since I wouldn't have bought the game just for that).

Three:
King's Quest games (original versions of all but II, I-VI CD collection, and I-VII collection on Steam).

Two:
Super Mario Bros. 2 (NES, GBA)
Dragon Warrior III (Both NES. Lent my copy to a friend, who lent it to a friend, who ran away from home).
Final Fantasy (Both NES. First one broken by a beach ball landing on the console while it was playing).
Ys III (PC Engine and Windows).
Legend of Heroes (PC Engine and Windows).
Legend of Heroes IV (Windows, and the PC-98 version I got from one of McCall's bake sales).
Xanadu (Saturn and PC-98).

By the way, if you've never played it, Xanadu is a lot of fun. And the (fairly limited) text is all in English for some reason.

So, this Buyinex -- will it help me to buy stuff with greater vigor and endurance?

FOUR

Chrono Trigger: SNES, PSX, DS, Virtual Console
Final Fantasy III/VI: SNES, PSX, GBA, Virtual Console
Grand Theft Auto: San Andreas: PS2, PC (retail), PC (Steam), XBLM

THREE

Crazy Taxi: DC, PSP, PSN
Final Fantasy II/IV: DS, Virtual Console, PSP
Lunar: The Silver Star: PSX, PSP, PSN
Shenmue II: DC (Japanese), DC (European), Xbox
Super Mario Bros. 1, 2, 3: NES, Virtual Console, Wii

TWO

Angry Birds: PS Mini, Android
Castlevania: Symphony of the Night: PSX, PSN
Dragon Age: Origins: X360, PC (Steam)
Elder Scrolls IV: Oblivion: X360, PC (retail)
F.E.A.R.: PC (retail), PC (Steam)
F.E.A.R. 2: X360, PC (Steam)
Fallout: PC (retail), PC (GOG.com)
Fallout 2: PC (retail), PC (GOG.com)
Fallout 3: X360, PC (retail)
Final Fantasy V: PSX, GBA
Final Fantasy VII: PSX, PSN
God of War: PS2, PS3
Grand Theft Auto III: PS2, PC (Steam)
Grand Theft Auto: Chinatown Wars: DS, PSP
Grand Theft Auto: Vice City: PS2, PC (Steam)
The Legend of Zelda: A Link to the Past: SNES, GBA
The Legend of Zelda: Ocarina of Time: Virtual Console, 3DS
Mass Effect 2: X360, PC (Steam)
Pilotwings: SNES, Virtual Console
Plants vs. Zombies: XBLM, Android
Resident Evil 4: GC, Wii
Resident Evil 5: PS3, PC (Steam)
Shatter: PSN, PC (Steam)
Shin Megami Tensei: Persona 3: PS2, PSP
The Sims 2: Castaway: PS2, Wii
Star Wars: Knights of the Old Republic: Xbox, PC (Steam)
Street Fighter II: SNES, PSN
Street Fighter IV: X360, PS3
Super Mario World: SNES, Virtual Console
Tetris: GB, Android
World of Goo: WiiWare, PC (download)

Is buying a second version of a game even unusual?  I do it often nowadays, partly because I bought a new computer recently and want to experience the PC versions of games that I already have on consoles.

The inclusion of Final Fantasy IV on my list is particularly silly, since in the case of this game I have three versions of a game that I have played zero times.

In compiling this list, I noticed an interesting absence: Secret of Mana.  I consider it, Chrono Trigger, and Final Fantasy III to comprise the SNES RPG trifecta, but I haven't downloaded Secret of Mana from Virtual Console.  I think that the reason is that although Secret of Mana has not exactly aged poorly, nothing about it is unique enough to have survived the passage of time, save the music.

I look forward to updating this list after Resident Evil 4 HD is released.

remember back in the NES/GB era, many companies released the original on the NES, and a striped-down, 8-bit monochrome version on the GB? like with Mega Man, or Donkey Kong Country vs. Donkey Kong Land? stuff like that.

other than that, the only time ive bought a game twice was on its original system, and then on wii virtual console, after having gotten rid of the original system some time ago.