The most mind bending games for me, Manhunt and The Suffering.
Manhunt for its brutality, it is the only game i can think of that took violence at the time, beyond what Rockstar was doing with GTA series.
The Suffering, for its historical references that made you question what if the experiments on inmates actually happened.
The biggest game to screw with your head that hasn't been mentioned yet is IMSCARED (I heard there's a new extended version on Steam as well).
Basically, it's a psychological horror that breaks the 4th wall by crashing at certain points, and altering your computer (desktop background, file dropping, that sort of thing).
Oh my god, no one mentioned Ori and the Blind Forest OST! I feel heartbroken!
As for mind-fucking games:
Portal - as has been mentioned, this was the first time a game messed with my head
but one that hasn't been mentioned:
The Talos Principle - Kept me guessing all game until the very end. Amazing writing and a great concept
As mentioned in some replies above Stanley Parable is a good example.
Braid has twist to it.
I see that people have very different ideas about what the term "mind-bending" means...
Also, I'm drunk...
I'll cast another vote for Bioshock Infinite, also I thought Transistor was kind of mind-bending.
Mind Bending game that comes to my mind was Doom 3 late and night in a dark room with headphones on.
For me, the twist in Star Wars: Knights of the Old Republic was something I probably should have expected, but took me completely off guard. It's not mind bending throughout the entire game, but when the truth is finally revealed I was like WTF?!
Killer7. I'll just leave this here in support of my argument.
Listen carefully. Yes, it is English. Yes, it is intentional.
nah it was obvious. not even halfway through i figured it out.
shin megami tensei nocturne was pretty out there.
Always interested in playing this game since it was made by Suda51 (No More Heroes director) yet don't want to be spolied by everything it has to offer.
In my opinion especially for the time it doesn't get any better than this. Especially the sound from Act I
My two most "mind fuck" titles of recent years would probably be the Stanley Parable and Hotline Miami. I don't know if Id quite call them a "mind fuck" but as far as video game plot goes. It defiantly had me in the "WTF" mindset. Then again I was drunk during the majority of both :P
Oxenfree gets pretty fucky. Not in terms of plot but in terms of that "there's something fucking with you" feeling and the "it knows what I'm going to do even though I have choices" feeling. 2D horror sounds like a joke but this game is incredibly well put together. I highly recommend it.
Bioshock infinite's DLC was pretty mind fucky. The 2nd episode of burial at sea gave you a better look into the world that was much more linear in the original game. If you played infinite and didn't play burial at sea you are seriously missing out. I would argue that episode 2 of burial at sea is better than the original game in terms of gameplay and story. If you disliked the turn away from survival horror that took place in infinite then you'll like this DLC.
Oh hell yeah! If the music creators for that game had better options for sound we would have been listening to it on the radio.
Most mind-bending game? Off the top of my head I'll have to go with HellCab.
For a more recent entry, I'd pick Calendula