Here are the ones that I know for sure:
-Eclipso (who you've already referenced)
-Dr Polaris (guy with purple shirt and blue cape)
-Major Force (guy with purple and yellow outfit)
-Girder (dude with "LIVE RUST" written on him)
-Atomic Skull (dude that has a glowing skull for a head)
-Blackbriar Thorn (the wooden guy that fights Alan Scott)
-Mammoth (huge dude with red beard)
-I think that Da Bomb might be the one that took out Power Girl. He showed up in the previous JSA series. He's basically a nutso villain with a serious infatuation with Power Girl.
-Also Hellhound may be the guy thats controlling all of those fire breathing dogs, but that's just a guess.
-Blue Moom, Tiger Moth, and Tapeworm get named, but I honestly had never heard of them until this issue. Does anyone if they are original characters?
-The guy with the 2 swords and a shark looking face looks very familiar but I can't recall his name.
It used to be comics would include a little recap of how a villain you thought was dead survived, but now villains just pop up with no explanation. I could have sworn that Major Force was dead.