I never used to be terribly interested in Achievements. My friends were into them and occasionally played games in order to get the achievements, not to have fun. The obvious games that showed this were Avatar, Terminator, and other miscellaneous children's games of children's movies. I believe this is what originally put me off of the idea as well as my involvement in another forum community that generally looked down upon achievements in games. 
 
Recently, this has begun to change. I blame it on joining Giantbomb and how achievements are often discussed and linked to one's profile. I have begun to chase after achievements in games after I would usually have put it down and it has added some needed replayability to what would otherwise resemble someone suffering from ADD's playing habits. And so, tonight I have achieved my first S Rank. 
 
Bull: Scholarship Edition. I saw it on the Xbox marketplace for 360 games and, since I had a Visa giftcard, as well as having originally played it on the PS2 without finishing it, I decided to shell out the $20 for it and have a good time. It was not as good as I remembered but it was still fun enough for me to play through it to get all of the achievements, one of which was to get 100% in the game. That particular achievement was the most painful due to the Errand glitch (errands, which add towards the 100% can stop showing up and the console needs to be reset a couple of time until they start showing up again, only for a couple of them though and the loop restarts) as well as one of the jobs I completed not adding it's percentage to the total and I had to redo that job. The final time count came out to 20-25 hours in my estimation. 
 
What was your first S Rank?

Not really a big on getting a S-rank but  Castlevania: Symphony of the Night was my first. I knew this game inside out from playing this on the PS so the achievements were easy for me to get. Still one of my favorite games to play.

Mine would have been Bioschock, had the extra one not been added. As it stands, my first one was Dead Space, of all things. I'd have more of the damn things if my 360 was online, but it's probably for the best that I don't have access to all those deliciously easy-to-access downloadable games.
 
Congrats, btw! :)

It will be Fallout 3. I'm one achievement away (collecting all the alien recordings) from finishing everything up, and I really just have to force myself away from the rest of the game to go get it.

My first S Rank? I think it was that old Tomb Raider game. Of course I have 126,000 gamerscore so... I have about 100 S Ranks now, but I think that was the first...

" Mine would have been Bioschock, had the extra one not been added. As it stands, my first one was Dead Space, of all things. I'd have more of the damn things if my 360 was online, but it's probably for the best that I don't have access to all those deliciously easy-to-access downloadable games.  Congrats, btw! :) "

I only have 3 S rank games. All of which was easy. I could have easily gotten an S rank on Call Of Duty 4 if it was not for that stupid fucking achievement glitch. I've got all 30 intel but it says I have not got 15 intel.
 
Fight Night Round 3 
LOST: Via Domus 
Assassin's Creed II

Oblivion. I have never played a game so damn much in my life, Fallout 3 is catching up but those damn Karma achievements are holding me back.

Probably Oblivion, the achievements there were very easy to get.

" I only have 3 S rank games. All of which was easy. I could have easily gotten an S rank on Call Of Duty 4 if it was not for that stupid fucking achievement glitch. I've got all 30 intel but it says I have not got 15 intel. Fight Night Round 3 LOST: Via Domus Assassin's Creed II "

Mine was Doritos Dash of Destruction. :|

Assassins Creed - yes I went around and got all th stupid flags... but then I'm a sucker for collecting in an open world... (I S-Ranked The Saboteur which means you do 1200+ side mission/blow up/pick up/twiddle things. Yeesh.)

My first one was RE5, but when the first DLC came out I lost it.
 
Later I got the MW2 S-rank.

Viva Pinata!

"Viva Pinata! "

I've noticed getting more into achievements thanks to GB as well.
Got only 4 so far, in order:  Fight Night, After Burner Climax, Monkey Island 2 and Dead Rising: Case Zero. OK that's 3 XBLA games so maybe not the most difficult ones. 
Determined to get S-rank on Mafia 2. Only difficult there is the driving one on the DLC. Will take a while

retail was Lego Batman :D

Mine was the original Assassin's Creed. Yeah, I got those flags. Then ACII, most recently finally eked out CoD4:MW.
 
I've got none for XBLA games yet.

" Mine was Doritos Dash of Destruction. :| "

Mine was Castlevania Symphony of the Night. Love that game.
 
The only S Rank I am ashamed of is TMNT, lol.

My first s rank was Shadow Complex. I just got into 360 around Feb.

How many S-ranks you have tends to be proportional to how much you like Arcade games, because it's often a lot easier to 100% the achievements on them. The only arcade games I own are 'Splosion Man and Geometry Wars 2 so they're a bit more difficult. 
At least it's now a bit more possible to get S-ranks on retail games, anyone remember the "Be the best in the world" achievement on GRAW?
 
My first, and only so far, S-rank is King Kong. Incredibly easy S-rank (you just beat the game... O_O)  but I did actually enjoy that game, unlike people who bought Avatar (the airbender one) to get the 5 minute S-rank thing.

S-Ranks in this order:- 
 
Monkey Island 1 
1 vs 100 
Fallout 3 
Oblivion
Dash of Destruction 
Assassins Creed II 
Sherlock Holmes vs Jack the Ripper 
Batman: Arkham Asylum 
Dead Rising 2: Case 0 
Dark Void 
Costume Quest 
 
I have to say though that the only one that feels like I really had to work for it is Arkham Asylum, the others all came from just an investment of time in a game I enjoyed. All apart from Dash of Destruction. That kind of gives away a streak of achievement whore in me! I do have about 5 others which are close (alan wake, mass effect 2, darksiders, forza 3) and I would have things like MW2 and L4D2 but I'm not so bothered by them to find people capable online in forums or anything.

Very first S-rank (at 12 currently) was Mass Effect. I don't regret a single hour of time spent in that game. (Mass Effect 2 is also among my S-ranks)

Deathspank. Read it and weep!

I believe it was Prince of Persia, including the Epilogue DLC

I only have 2 S-Ranks .... Mass Effect 2 and Costume Quest ..... what can I say I move on quickly .... except for the games I really luv , yet got tired of trying to have all achivements in Orange Box (and the fact that I do not play team fortress ) 

I have about 8 games that are 1 achievement away from S-rank, and they're all damn near impossible. 
 
They haunt me day and night.

" Mine would have been Bioschock, had the extra one not been added. As it stands, my first one was Dead Space, of all things. I'd have more of the damn things if my 360 was online, but it's probably for the best that I don't have access to all those deliciously easy-to-access downloadable games.  Congrats, btw! :) "

Oblivion was my first, and although that was rudely taken away from me by DLC, I did manage to claw it back after completing The Shivering Isles recently. 
 
After that I also did LEGO Harry Potter and Dead Rising 2: Case Zero. Both pretty easy if you have a guide to hand.
Xbox 360 Achievements is a great website if you need help getting those last couple of points in a game.

My first was Pac-Man: Championship Edition (which is pretty easy and a great game BTW). I followed that up recently with the shameful Dash of Destruction (Doritos game).  
 
Next on the list is Assassin's Creed 2, which I'm pretty close to. The hardest thing left is the 100 feathers, but I have all of them except the ones in Venice. I'm using a guide, and it actually goes pretty quickly.  After that the remaining cheevos are pretty easy. If only I could drag myself away from New Vegas to finish them...

My first was Shadow Complex.  I only have 5, all XBLA games.  I've come close to some retail games, but generally there's at least a few achievements that would be far too frustrating or time-consuming to attempt.  Too many games out there to waste time on one.

I was going to get an S-Rank in Halo Reach almost, but apparently because of the update I will drop down from my current A-Rank. I currently have 2 left.

my first S rank was the godfather 2 game.

" Mine was Castlevania Symphony of the Night. Love that game. "

My first? COD4, you couldn't imagine the feeling of beating Mile High Club after trying for 30+ minutes straight to finish it on veteran.
 
However, I think that it doesn't matter what your first S-Rank is, but what your favorite S-Rank is. Shadow Complex, Borderlands (without DLC), and Batman: Arkham Asylum come to mind as examples of fairly easy but also very fun S-Ranks.
 
Also, I bought Madden NFL 06 and returned it before I got a single achievement, think on that.

My first (and only thus far) was 3 on 3 NHL Arcade.
 
It's a pretty easy 200 points / S-Rank for those of you that are really into achievements.

Ultimate Sega Mega Drive Collection. 
 
Laughably easy S-rank.

Virtua Fighter 5.

" @ProfessorEss said:

"Viva Pinata! "

ME TOO!!!!!  I just wish the second one didn't have all of those achievements linked to trading stuff with others. "