1. Superman vs Captain Marvel:

This one makes the top of my list because it succeeds in not only showing an epic battle between Superman and what was originally another comic book company's superman, it also cast Superman in the role of "the bad guy." Not willing to take Luthor at his word (which is understandable), Superman attempts to destroy a device underneath Luthor's new Lexorcity because he thinks it's a bomb. Captain Marvel suggests that they call the Atom down from the Watchtower to check it over first and from there, things turn violent. I think what makes this fight particularly brutal is the fact that these two are usually portrayed as "nice guys." Superman is particularly vicious toward Marvel in this fight. (The fact that we, the audience, know that Marvel is actually a little boy also hightens the brutality.) Lexorcity is demolished as a result of the fight and we also see shades of Kingdom Come toward the end, when Marvel uses his magic lightning on Superman.

2. The Flash vs "Lexiac"

Every once in a while, the Flash does something that makes all the other superheroes look on and go "damn." They then start wondering if Wally is actually the most powerful superhero. Such is the case when Flash single-handedly destroys the Lex Luthor/Braniac merger that I'm refering to as "Lexiac" here. Flash appears to retreat from Lexiac, only to barrel into him from behind... and with enough momentum built up to destroy part of Lexiac's armor with each pass. Then it's revealed what Flash is actually doing... he's running along the circumference of the Earth in order to pick up enough speed to hit Lexiac with each pass. There's literally nothing Lexiac can do about it. When he's done with that, Flash vibrates his hands into Lexiac and drives the Brainiac components out of him. Most of the fights on my list involve Superman, but this one is second because it's awesome and does not involve Superman.

3. Justice Lord Superman vs Doomsday

A ruthless version of Superman fighting a surprise appearance by Doomsday (the monster famous in the 90's for temporarily killing Superman). Particularly brutal, the fight actually does start off with the Justice Lords fighting him, but it comes down to just JL Superman in the end. Clearly, Doomsday seems to be the more durable. At one point, the two hit each other at hypersonic speed, much like in the famous comic book, creating a shockwave that blows out windows for blocks. Doomsday is left standing while JL Superman is on the ground, stunned. It is only through the use of heat vision to cook Doomsday's brain that the Justice Lords come out on top. (We later see evidence that this is how the Lords dealt with all of the supervillains in Arkham Asylum in their world.) Lois Lane, voiced by Dana Delany, sells the momeny by saying "You lobotomized him? It's so out-of-character..."

4. Question vs "Lexiac"

Question appears in Lex Luthor's office at LexCorp and attempts to murder him. While he doesn't even come close to succeeding due to Lex secretly having been merged with Brainiac at this point, the mere fact that Question was going to go through with the idea of assassinating him so that Superman wouldn't have to is chilling. The whole episode really belongs to the Question, but the confrontation with Luthor is on my list not so much for the fight itself but for Question's words just before the short fight begins. Yeah, it was very "Rorschach" of Question to do this... but Superman did mention during the show something to the effect that Question wasn't thinking clearly and was delusional with fatigue.

5. Superman vs Darkseid

This would make the top of many other people's list. Superman is taking punches from Darkseid and decides he isn't going to take it anymore... beginning to hit Darkseid much harder than Darkseid appears to be able to hit Superman. This eventually forces Darkseid to use other methods to fight back, but Superman makes his point. And therein lies why this isn't #1 on the list. Superman makes his point in what I consider to be a ponitification at the beginning of the fight that takes way too long. That ruins much of it for me.

6. Batman vs Justice Lord Batman

Interesting confrontation with Kevin Conroy doing both voices. At one point, you really can't tell which Batman is saying what. It ends with JL Batman stating that they (the Justice Lords) have created a world where a 10 year old boy would never lose his parents because of a punk with a gun. Hearing this, Batman surrenders.

7. Lobo vs Kaliback

Short. We dont see much except the last few seconds of it, where Lobo starts pitching cars on top of Kalibak until he can't move. Lobo says "Say it! Say it!" Kalibak replies "Uh... Un... Uncle." Lobo's got one more car and he's aiming for Kalibak's head when Hawkgirl flies up to him and tells him that he's beaten and to put the car down. A funny little moment. (Lobo was attempting to fill Superman's position on the team after he had apparently died.)

8. Superman/Huntress vs Cadmus

Simularly funny in that you have Superman doing all the "heavy stuff" while Huntress basically takes care of stragglers. I love the fact that she wouldn't let him take all the action.

The Captain Marvel/Superman fight was awesome. I also liked the cage match in "Grudge Match" with Wonder Woman, Hawkgirl, Vixen, etc.

Great list. Many of those are favorites of mine too.

Some other favorites:

Luther/Flash vs. JL: Good mix of action and humor.

Superman vs. Amazo: Like the action and the music that goes with it.

Wonder Woman vs. Black Canary/Vixen/Huntress/Hawkgirl: One of the most brutal fights on JL.

MM/Shining Knight/Vigilante/Atom Smasher vs. Suicide Squad/Annihilator: Lots of fun skirmishes. "Ask yourselves: 'Is being in here with me what you truly desire?'"

That's the one!

Excellent choices so far!

Metamorpho vs the JLA in "Metamorphosis: Part 1" was great as well.

That fight in Roulette's secret ring was awesome.

That Wonder Woman reveal was possibly the best "Oh shit" moment in the series.

That's certainly what I said when she showed up in that ring.

Followed by, "They are all so completely screwed."

I was going to put that one in the list, but I thought I'd leave it out for others to contribute.