He was vulnerable to “magic” pre-Crisis; I’m not sure if this is still true, or exactly how it was defined.
Post-Crisis, I know he does have a need for oxygen. He can go much longer than a human without breathing, but not indefinitely; he needs to take a breath and hold it in before traveling in space, and he knows that he needs a ship to travel more than a certain distance.
What is “Crisis”? Is that his death?
Superman is still vulnerable to magic (but only as vulnerable as the next guy, a point some writers forget). A spell, or properly enchanted weapon (Wonder Woman had a sword made by Hephaestus in Kingdom Come that could cleave electrons and cut Supes) could kill him.
Radiation from a red sun (or, failing that, snuffing out our sun) has also sapped his powers, but that doesn’t kill him per se, but then you could kick him to death, or shoot him, or something.
Starvation, dehydration, and asphyxiation could all work (post-crisis), but he can fast and hold his breath for much longer than a human. Would have to hold him in a vacumn for hours (he’s flown to teh moon and back on one breath), and without food for years, I’d guess. You could also just beath the ever loving crap out of him (a la Doomsday). Put him at ground zero for several consequitive multi-megaton nuclear strikes, then follow up with a super-strng meta-human assault, and you’d have him.
The Crisis, or more properly, *The Crisis on Infinite Earths, was a major event in the mid 80’s that involved all the DC comics titles. It destroyed quite a few of the alternate earths floating around at the time, and merged the survivors together.
Many writers took the oppurtunity to reboot their books or at least significantly change the history of their characters. Superman is probably the best example. He was significantly depowered (Pre-Crisis: I Juggle planets! I fly through the sun, to clean my cape! Post-Crisis: I can barely lift a battleship over my head! Atomic bombs sting me!), and his history was changed (he never had a career as Superboy, for example).
Depowering him was a really good idea story-wise because if he’s totally invulnerble to everything but kyptonite, the villan must always take hostages or create some crisis elsewhere to distract him. It also just occured to me that superman could pobably compress thousands of liters worth of air into his lungs which would partly account for his ability to go without breathing for so long.
Dunno if it’s true anymore, but post Crisis, he seemed somewhat vulnerable to sonic and electrical attacks as well.
It also seemed that his invulnerability has or had two levels: His super dense body made him phisically invulnerable, and he could also resist shock and pain by concentrating. He could be hurt, or even knocked unconsious, by a surprise attack.
However, it seems that his powers have once again been enhanced. Pity, i thought it was kind of cool that a planned, tactical attack by mere mortals could defeat Superman.
Of course, Post-Crisis, one of the big changes was that Kryptonite was much more rare than in Pre-Crisis continuity, since it wasn’t needed as a MacGuffin anymore. In fact, originally, there was only one piece of Post-Crisis Kryptonite, though there have since been several other pieces sighted.
The “vulnerable tomagic” thing was always an acknowledgement that his powers were at least superficailly based on scientific principles. As Menocchio says, the point was that no amount of physical invulnerability could overcome magical effects. However, Pre- and Post-Crisis, it’s often been used as an achilles heel unique to Superman, which is incorrect.
In the new Justice League cartoons, they seem to have given Superman a special vulnerability to electricity. In one of the first episodes, an electric shock from a booby-trapped manhole cover renders Supes momentarily unconscious.
The Superman animated series (the recent one) had a whole string of aliens that were on Superman’s level. Lobo could go toe-to-toe with him, and Darkseid pretty much turned Superman into his bitch.
I always wondered why Supermen never ever got found out, despite it being pretty obvoius. Look, he’s wearing freaking glasses, OK?
Geez…
He radiates a mild field of stupidity.
Pre-Crisis, there was an issue that dealt with this. Turns out Superman had the power of “super-hypnosis.” His super-hypnotic trance was so pwerful that it was constantly switched on a little bit. Since, while dressed as Clark Kent, Superman wanted to project an image of himself as “mild-mannered,” his super-hypnosis made everyone think he looked like a pantywaisted little weak sister. His super-hypnosis was so super that it even worked on photographs and through the TV.
Post-Crisis, Clark just keeps a weight bench in his apartment.