In the comics, how many different Superman have appeared or existed? Are there any big differences between those different versions of Superman?
As indicated in the comments, there have technically been hundreds (at least) of different versions of Superman. In the 50's and 60's, it was common for the Superman family of comics to include "imaginary stories", stories that were explicitly not considered as featuring the same Superman as appeared in regular stories. Think of it like the Simpsons "Treehouse of Terror" Halloween shows. Superman might have new powers, or be married to Lois (or Lana, or Lori Lemaris; pretty much anyone with an alliterative name that started with "L"; except Lex Luthor - 1950s and 1960s, remember?). So, for now, let's ignore these (usually) one-off alternates.
Starting in FLASH #123, the DC multiverse was officially born. With that, we had an Earth-1 Superman, an Earth-2 Superman, and the evil Ultraman of Earth-3.
The Crisis on Infinite Earths (1985-86) destroyed most of the multiverse, and rolled several worlds together into one. This brought us the Post-Crisis Superman. While the multiverse was eventually recreated, we mostly saw it populated by characters from one-off stories, or variations on the themes above.
Then, Flashpoint changed the DC Universe again, and gave us a "New 52" Superman that had notable differences from the Post-Crisis Superman. With Rebirth, we saw the Post-Crisis Superman returned; and now, I believe that the current Superman is some sort of amalgam of these last two (with the emphasis on the Post-Crisis version, as he's still married to Lois, and still has a son with her).
So, let's cover the golden age Superman (Earth-2), the silver age Superman (Earth-1), the post-Crisis Superman, and the New-52 Superman.
Golden Age, Silver Age: over the course of the first 2 years of his publishing history, Superman picked up various new/enhanced powers, and had various small alterations in his environment. Unlike most characters, Superman was continuously published from the late 1920's through today. So, when Earth-2 and Earth-1 were set up, they distinguished the Earth-1 Superman from the Earth-2 Superman mostly by keying into these changes that had happened over time.
Post-Crisis: John Byrne was selected as the writer (and main artist) to launch the post-Crisis version of Superman. He reined back in the character's powers to some extent (although later teams tended to expand them again). From 1986 through Flashpoint in 2011, Superman's story was much more coherent and consistent than it had been prior to that point.
New 52: Grant Morrison's stories reintroduced Superman in the post-Flashpoint "New 52" era. There were a few adjustments made (reversing some of Byrne's points).
I'm just going to hit some of the most notable differences in the character's history and powers. Unless otherwise stated, all version have powers including enormous strength, flight, invulnerability, super-speed, heat vision, x-ray vision, etc.; and all came to Earth from Krypton, and had a long-term romantic relationship with Lois Lane.
Golden Age Superman: His powers were generally scaled back a little, often using the theme from the 1950's SUPERMAN TV show as the rough limits: faster than a speeding bullet, more powerful than a locomotive, able to leap tall buildings in a single bound (I believe they did leave him able to fly, actually); he could be hurt by powerful enough explosions or weapons.
As far as personal background, I don't believe he had any significant memories of Krypton. His birth name was Kal-L. His adoptive parents were dead by the time he first appeared as Superman. He adopted his identity as a young man; he had not been Superboy as a child. In the 1970's, we found out he had eventually (sometime after we started reading about the Earth-1 Superman in the comics) married Lois Lane; they had no children. He and Lois worked at the Daily Star. His cousin, Kara, came to earth in a sentient space craft, arriving long after he did; she became Power Girl. He was thought to have died in the Crisis, but actually survived until the INFINITE CRISIS crossover, as did his Lois.
His strangest ability, unique to him, was the ability to mold his face to look like someone else (only used in a few stories in the 40s).
Silver Age Superman: This is the Superman that the Christopher Reeve movies were based on. He had near boundless strength and invulnerability; he not only could fly, but could fly through space unaided; and he had heat vision and freeze breath. His costume was made from blankets in his spaceship - being from Krypton, this made the costume invulnerable.
Kal-El was sent to Earth by his parents, Jor-El and Lara, as an infant, just before Krypton exploded - and somehow, this seemed to draw a significant portion of the exploded planet, plus almost any space debris in its orbit, to the vicinity of Earth (eventually). His teenaged cousin Kara had lived in a city on an intact fragment of Krypton; however, that eventually broke down, and she was sent to Earth so he could take care of her; she became Supergirl, of course. His adoptive parents, Jonathan and Martha Kent, died when he was a young man (at least 18, less than 22). He had a career as Superboy as a pre-teen and teenager. His pet dog from Krypton, Krypto, showed up during this time. He met time-traveling heroes inspired by his legends during his Superboy period; they were called the Legion of Super-Heroes, and he frequently travelled into the future and had adventures with them. He dated Lois Lane (sometimes as Clark Kent, more often as Superman), but never married her. they worked together at the Daily Planet (except for a period during the 70's and 80's where they also worked for a Metropolis TV station, WGBS - Clark was a news anchor).
He had a number of strange abilities. The oddest was "super-hypnosis" (which he used sub-consciously during the new broadcasts, to make Clark seem smaller and thinner than Superman. My personal favorite strange ability wasn't generally identified as such, but in practice he tended to look ludicrous while using it. You seem, he could move planets out of (or back into) their orbits; which he would apparently do by simply using flight and strength together, and pushing the planet. One can imagine seeing him while he was doing this, and coming up and asking him why he seemed to be straining so much to do that handstand....
Post-Crisis Superman: His basic power set was the same as the Silver Age Superman. Initially, the powers were toned down (for instance, couldn't survive in space without oxygen), but eventually ramped back up to almost the same level as his predecessor. However, his powers were more thoroughly explained (with pseudoscience, but still). He was a solar power battery; keep him in the dark long enough and his powers fade to basically nothing. Rather than actually being invulnerable, he basically had a force field surrounding him (this kept the bulk of his costume (except the cape) from damage, most of the time).
Sent from Krypton as an infant; named Kal-El; adopted by Jonathan and Martha Kent. Uniquely, his adoptive parents were both alive well into his adulthood (Jonathan died in the mid 2000's). No career as Superboy or ties to the Legion (some sort of tie was re-established in the mid 2000's, but without an indication of a career as Superboy in his youth). Like the Golden Age Superman, this version not only dated Lois Lane as Clark, but married her. They both worked at the Daily Planet. He got a Kara and a Krypto, but (again) not until the 2000s. Prior to Flashpoint, he and Lois had a kid named Jonathan in their life; he was at least part Kryptonian, but was not their son. When the character came back on-stage post-Crisis (coming out of the Convergence event), they now have a son named Jonathan.
The most unusual thing about his powers was the explanations as to how they worked, which were covered above.
Finally, the New 52 Superman: powers seem to basically match up with the Post-Crisis Superman (except maybe the force-field style invulnerability, as his outfit does seem to take a bit more of a beating).
Kal-El; Krypton as an infant; Jonathan and Martha Kent; no career as Superboy; Kents died wen he was a young adult; Daily Planet; romantic interest in Lois; cousin Kara. With the advent of the Rebirth event, this Superman and the matching Lois Lane both died. However, the "Post-Crisis Superman" and his wife Lois appeared from the multiverse. The essences of both versions of these characters were merged somehow; I expect that the resulting characters will be more post-Crisis than New 52, but time will tell.
Other variations of some note include:
- The titular character of three recent "Superman: Earth-One" graphic novels;
- Kent Shakespeare (intended to take his place in the Legion, initially);
- The Earth-Prime Superboy (locked away with golden age Superman from Post-Crisis to Infinite Crisis)
- The older version of the Post-Crisis from the time of BATMAN BEYOND (sometimes referred to as Superman Beyond).