Morrus said:
I don't know a great deal about the others (apart from Batman), but how tough are they? The Flash, Hawkwoman (Hawkgirl?) etc., all seem to be exactly as tough as Superman when it comes to resilience.
In the comics:
The Flash, as far as toughness goes, is pretty much a normal guy. His resistance to damage comes from his control of the Speed Force (he can move momentum around, so he could steal the kinetic energy from a series of gunshots - this is something you never see him do in the cartoon, probably because it would take too much time to explain), from his ability to simply dodge a shot, to his superfast healing ability. Catch him 'flatfooted', though, and he's pretty much a normal Joe.
Hawkgirl, I'm not too sure about. I know nothing about her most recent comics incarnation, but she used to be just a slightly stronger than normal person (I think Thanagarians were more resistant to damage and stronger than humans) with the artificial wings. Interesting note: She uses a mace because using archaic weapons used to be a trademark of Hawkman's.
The Martian Manhunter. Christ on a pogo stick. MM is just as tough as Superman, plus he has about a dozen superpowers that Superman doesn't.
Wonder Woman. Extremely tough, though she can be cut, shot, etc when she's not aware of a threat enough to block it. Depending on who is writing her, she can be anywhere from 'tossing a locomotive around is no problem' strong to 'I am at least as strong as Superman' strong; more so if she's using the lasso or the material her invisible plane is made from.
John Stewart. OK, if there is someone who simply gets no love in the cartoon, it's poor ol' John. Like the Flash was almost a comedy-relief figure in first season, ol' John has only recently remembered he can use that ring for things other than making shields and the occassional hammer. A Green Lantern ring is rightly called The Most Powerful Weapon in the Universe. In the comics (where at least for now the current GL is Kyle Rayner) the Ring can do pretty much anything; Kyle's done solar-system-level telepathy, opened stargates, created matter, helped Wonder Woman move the moon, etc. All that lasts as long as he concentrates or knows a threat is there, though; he's been blindsided, shot, stabbed almost to death, etc.
Part of the confusion comes from the fast and loose application of abilities in comics themselves. Sort of an unwritten rule (along with many others) is 'in your own book, you are The Man'; when you're guest-starring in someone else's book, you may or may not be The Man. The JLA book is suppossed to showcase the heroes being just the absolute best heroes Earth has to offer, so they do a lot of things that are very over the top (like the aforementioned moving the moon thing), feats that even in their own books they may not do.
More than likely the cartoon simply tones things down to the point where they have a viable story that can be credibly told in the time they have. It's best to just think of the cartoon as it's own island of continuity that only has a loose connection to the comics universe.