So much cuteness and nice nods to canon. I'm putting these under the cut for those that want to be surprised in the game. So some SPOILERS AHEAD.
For some reason the iconic JLI isn't together under the team name. There's members like Blue Devil in that list and they also have Extreme Justice. While many wives appear in the game (Animal Man's whole family are present) Sue isn't around although Ralph's bio mentions her.
Maxwell Lord: I've seen him as a bad guy in the Checkmate outfit but haven't tested him yet.
Guy Gardner: During the Oa attack there are several shots of the Green Lanterns fighting off bad guys. Guy is shown for a split second reclining as his constructs battle asking if their ready to fight. He's also seen doing one of the missions around the levels. Standing at some table with different types of food he claims to have made (you made the radish Guy?) and wanting someone or something to eat it. If you get a suitable being to eat it he brags that he knows they liked it because he made it. I tried to take the item once to give it to someone and he attack me for stealing. I gave it back and he said "that's more like it." I have had all the Earth GLs together but at one point I left Guy and Hal alone to fight a bad guy while I finished a mission. When I got back they were fighting each other.
Ice: In her JLGL/new 52 costume. She's ideal for putting out various flames but will attack any poor soul on fire until they die. Hearts appear above her and Guy's heads when they are near each other.
Fire: In her new 52 costume but flames on in battle.
J'onn: If you go to the JL headquarters the visitors will change. J'onn appears in the "JLI" set up and will mention his love for chocolate cookies. Usually when you create things for the characters in that level they won't react unless you create a threat. J'onn ate the cookie (that looks like a oreo if you type "chocolate cookie.") It's so ingrained into him that he stopped fighting the enemy to run toward the giant cookie I made, ate it and wanted more.
Ted: He appears at the headquarters like J'onn and the only thing he says is "Bwa ha ha." Ted uses his BB gun and the Bug is a vehicle you can use.
Big Barda/Mr. Miracle: Barda is at the HQ and while Scott's not she tells him that their leaving. Both have hearts above their heads when their near each other. This doesn't always happen with couples as Renee Montoya will have a heart and Batwoman will have a circle with a slash over the heart. And some don't have any emotion response. Nightwing will have this reaction with Barbara and Kori (he's the only one that I've seen that happily throws his arms up.) Kori will have hearts for Roy and Dick usually flying towards them. Roy does this with her too.
Booster Gold: At the HQ he shows up to give his usual "Booster Gold" talk. But he has another cameo that I liked more.
There are different sections of the game based on heroes home towns (Gotham has more than the rest) where you have to help them in the boss stages. In the Flash section the lead character Maxwell finds out his arch-enemy and Zoom are racing against Flash. He decided to join in to ensure nothing funny happens. Then the judge for the race turns up...it's Booster Gold. Barry groans and says "this guy." What makes it even funnier is comparing it to his slightly miffed reaction to facing against his foe in a charity race. Booster lays down the rules and says no cheating. Although it never mentions it in the game there's no way for Booster to tell because their racing at superhuman speeds, this is shown by the audience slowly moving during the race. After it's done Booster seriously talks to Barry telling him there will be no future if Maxwell doesn't win against his evil clone. Barry says Booster's a good guy to which he replies "yeah I know."
I'm paraphrasing but this was my favorite line Booster says: "Hello lovely ladies and less-handsome than me gentlemen!"
Rip Hunter: I'm mentioning him here because of his connection to Booster. I think my version is buggy because Rip is hard to place on the floor. Instead of falling onto it he sort of stays where he's at running in place trying to get to the right side of the screen. Only his gun stops the bad guys. Although the Time Masters don't exist in the index the Linear Men team does. Ironically it's made up Rip (wearing his Time Master Vanishing Point costume), Waverider and Liri Lee. Well it's ironic if you read TMVP otherwise it makes sense. Ah time travel. He's listed as Booster's son in his bio and for some reason the Time Sphere is listed as Booster's despite Rip creating it. When around Booster a picture of a man and woman holding hands goes over his head. It took me awhile to realize this meant family. Booster doesn't have this reaction around him which makes sense since he doesn't know their related.