Heck, I'll take a stab at this. You might think I'm off a little one way or the other for any particular title, but what's an R level among friends.

R2's:
Aliens Vs. Predator: Extinction
Arctic Thunder
Army Men: Major Malfunction
Arx Fatalis
Baldur's Gate: Dark Alliance II
Battle Engine Aquila
Battlestar Galactica
Bionicle: The Game
Black Stone: Magic & Steel
Colin McRae Rally 2005
Crusty Demons
Dakar 2: The World's Ultimate Rally
Dai Senryaku VII: Modern Military Tactics
Deathrow
Dreamfall: The Longest Journey
Dungeons & Dragons Heroes
Egg Mania: Eggstreme Madness
Fireblade
Gladius
Grooverider: Slot Car Thunder
The Guy Game
IndyCar Series 2005
Intellivision Lives
Jedi Knight-Jedi Academy
Kakuto Chojin
Land of the Dead: Road to Fiddler's Green
Marvel vs Capcom 2
Metal Slug 3
MX 2002 Featuring Ricky Carmichael
Myst III: Exile
Myst IV: Revelation
Operation Flashpoint: Elite
Otogi: Myth of Demons
Otogi 2: Immortal Warriors
Outlaw Golf & SeaBlade Bundle
Pro Cast Sports Fishing
Pure Pinball
Samurai Shodown V
Silent Scope Complete
Sphinx and the Cursed Mummy
Spikeout Battle Street
Spy vs. Spy
Still Life
Strike Force Bowling
Syberia II
ToeJam & Earl III:Mission to Earth
Tork: Prehistoric Punk
TransWorld Snowboarding
UFC: Tapout
Virtual Pool: Tournament Edition
V-Rally 3
Wakeboarding Unleashed Featuring Shaun Murray
Whiteout
Wings of War
World Championship Pool 2004
Worms 4: Mayhem
WTA Tour Tennis
Yourself! Fitness

Personally I'm not convinced that Kakuto Chojin was ever recalled, edited and re-released. I think if you come across any copy of the game and play track 23 from the sound options menu you will hear what sounds like Koranic verses. But there was one other bit of controversy about the game that I thought I would share. This is an excerpt from Dean Takahashi's book 'The Xbox 360 Uncloaked'.
"Ed Fries had sent Redmer to Japan to relieve Toshiyuki Miyata, the former Sony game studio chief whose big fighting game, Kakuto Chojin, wasn't in good shape. The staff was staging a mutiny and Miyata was leaving. Redmer had to undertake the controversial job of laying off many of the game developers in the office in a country where it is illegal to conduct a mass layoff. The job took him months to accomplish, and it was remembered as a big shock among the game developers in Japan."

R3's:
Air Force Delta Storm
Barbie Horse Adventures
Dragons Lair 3D: Return to the Lair
Frogger Beyond
Gauntlet Dark Legacy
Jurassic Park: Operation Genesis
Loons: The Fight for Fame
Pro Fishing Challenge
Steel Battalion w/controller
Steel Battalion: Line of Contact
Totaled!

Logically, I would have reasoned that Steel Battalion would easily have been the rarest Xbox game. How many chuckleheads would have ponied up $200 for a game? But from the figures I've read about, Otagi 2 actually sold fewer copies. Not that it matters much, as neither is particularly hard to find. But something that may interest those contemplating picking up Steel Battalion is that it was collaborated on by Atsushi Inaba of Clover Studios who seems to be the current cause celeb among game reviewers.

R4's:
F1 2001
Outrun 2006 Coast 2 Coast
Roller Coaster Tycoon
Tom and Jerry: War of the Wiskers

I've noticed that Ebay won't list The Guy Game and EBGames/Gamestop won't carry the 1st edtion GTA:SA. Not sure how much that affects their rarity, but it does hinder access and should be accounted for.

The Blockbuster exclusives:
Outlaw Golf: 9 Holes of X-Mas -R1
Outlaw Golf: 9 More Holes of X-Mas -R1
Outlaw Golf Holiday Golf -R3
Outlaw Volleyball: Red Hot -R1
Streetstyle Street Soccer -R1

The Toys-R-Us exclusive:
Sneakers -R2


I'm usually derisive of Platinum Hits versions, but at least these particular combo packs were exclusive to the Xbox and not trip over common.
Crash Super Pack -Wrath of Cortex & Nitro Kart -R2
Sonic Mega Collection Plus and Super Monkey Ball Deluxe -R2
Sonic Heroes and Super Monkey Ball Deluxe -R2
Shrek 2 and Shark Tale 2-in-1 Pack -R2

The Xbox never had a Platinum edition Super Monkey Ball Deluxe, so you get the regular version disc in the combo packs.




What follows has less to do with discussing rarity and more to do with things that might be of interest to Xbox collectors. You might like to keep an eye out for the ToCA Race Driver 2/Colin McRae Rally 04 bundle, Mace Griffon Bounty Hunter with bonus music sampler and World Championship Poker with the bonus Fundamentals of Poker Book. They're probably R2's at best, but they are variations from the regular versions.

Grand Theft Auto and Elder Scrolls III: Morrowind games both came with large fold out maps. These were the only Xbox game that I've come across that had anything extra inside, bonus DVD's, movie tickets, music CD's, collector cards, ect., that isn't clearly noted on the case.



Xbox Demo discs in DVD cases:
LucasArts Xbox Experience Vol. 1 Demo Disc -R3
Tom Clancy's Rainbow Six 3 Companion Demo Disc -R3
Volvo: Drive for Life 2005 -R2
Xbox Exhibition Vol. 1 -R1
Xbox Exhibition Vol. 2 -R1
Xbox Exhibition Vol. 3 -R1
Xbox Exhibition Vol. 4 -R1
Xbox Exhibition Vol. 5 -R1
Xbox Exhibition Vol. 6 -R3
Xbox Exhibition Vol. 7 -R2

EBGames/Gamestop Fable Limited Edition Bonus DVD. -R1
It's not a demo, but rather the exact same bonus DVD included with the Limited Edition Fable. Don't know if they were sold or given away, but they do have thier own unique case artwork and paperwork.



Xbox Live Starter Kit's cardboard sleeved Xbox games:
Xbox Music Mixer
Tetris Worlds Online
MechAssault
Project Gotham Racing 2
Crimson Skies: High Road to Revenge
Xbox Live Arcade’s launch disc with Ms. Pac Man

The Xbox Live Arcade launch disc was originaly sold by Microsoft for $4.99 in 2004, but I'm pretty sure it was later included in one of the 3 month Xbox Live Starter Kit's. The games were all sealed and though they are common now, I wonder how those cardboard sleeves will fare over time. There were also some demo's included in the Starter Kits for Whacked!/MotoGP, MechAssault/MotoGP, and MechAssault 2/OutRun 2.



Limited Editions, Collectors Editions, Special Editions, and GOTY's

These are in standard DVD cases:
Call of Duty 2: Big Red One Collectors Edition -R1
Fable Limited Edition -R1
Ghost Recon: Advanced Warfighter Limited Special Edition -R1
Jade Empire Limited Edition -R1
MechAssualt 2: Lone Wolf Limited Edition -R1
Elder Scrolls III: Morrowind Game of the Year Edition -R1
Robocop Collectors Edition -R1
Star Wars Starfighter: Special Edition -R1

Robocop and Star Wars Starfighter never had regular Xbox editions. The collector/special edition titles were merely marketing ploy's.

These are in DVD cases with cardboard slip covers:
Godfather Limited Edition -R1
Mortal Kombat: Deception Collectors Edition -R2
Need for Speed: Most Wanted Black Edition -R2

These are in metal cases with plastic slip covers:
Doom 3 Limited Collectors Edition -R1
Halo 2 Limited Collectors Edition -R1
Marc Ecko's Getting Up Limited Edition -R2
Splinter Cell: Chaos Theory Limited Collectors Edition -R2
True Crime: New York City Collector's Edition -R1

These are in cardboard box's:
Driver: Parallel Lines Limited Edition -R2
Robotech: Battlecry Collectors Edition -R4



Not for Resale: Limited Edition Packages (pack-in)
Sega GT 2002 & JSRF: Jet Set Radio Future (2002)
Star Wars: The Clone Wars & Tetris Worlds (2003)
NCAA Football 2005/Top Spin (2004)

Each came with a green bar on the cover identifying them as "Not for Resale: Limited Edition" packages. Each came with two seperate game manuals but both games were on a single disc. The disc's do not say "Not for Resale: Limited Edition" on them.

The 2002 Sega GT 2002 & JSRF Holiday Bundle included Amped: Freestyle Snowboarding. It came with a green bar on the cover identifying it as "Not for Resale: Limited Edition". The disc does not say "Not for Resale: Limited Edition"

The 2003 Star Wars: The Clone Wars & Tetris Worlds Holiday Bundle included Grabbed by the Ghoulies. It was the regular version of the game with a white sticker on the back of the case cover identifying it as "Not for Individual Sale". The disc does not say "Not for Individual Sale"

Not for Resale Editions (pack-in)
Halo: Combat Evolved (2004)
Came with a green bar on the cover identifying it as "Not for Resale". The disc also had a green bar identifying it as "Not for Resale".

Not for Resale Revente Interdite Package (pack-in)
Project Gotham Racing 2/Xbox Arcade (2005)
This came with a green bar on the cover identifying it as "Not for Resale Revente Interdite". It came with one game manual and two seperate discs. The disc's do not say "Not for Resale Revente Interdite".

Forza Motorsport/Xbox Arcade (pack-in) 2005
This came with a with a box on the cover stating "Includes Xbox Live Arcade". The disc itself is marked identically as the case cover.

I believe the Canadian's recieved some different pack-in games, such as Oddworld Munch's Oddysee/NFL Fever and Gotham Racing 2/Crimson Skies 2.
I haven't seen any of those first hand to verify though.



That's about it from me! From my personal Xbox data lists:
873 unique NTSC games
221 were games not found on the Gamecube or PS2
18 were, but received different titles
100 Platinum Hits versions


Lastly, I'd like to put in a good word for both of Dean Takahashi's books - 'Opening the Xbox' and 'The Xbox 360 Uncloaked'. To anyone even mildly interested in the Xbox, they are WELL worth your time. I bought the first book used to save some pennies and after I had finished it I made damn sure to buy his second book new because I WANTED to pay the man for his work! That's about the highest compliment I can give anyone.

Here's some street cred. You know I spent hours stacking them up like that and still I managed to get some upside down. Oh, poop!