So, the Young Justice Team is made up of young heroes who have older heroes as their mentors, right?
Are all the mentors and protegees actually known?
Miss Martian - Martian Manhunter
Wonder Girl - Wonder Woman
Artemis (Before death) - Green Arrow
There have been recent rumors about new members joining the team soon. Blue Beetle and Beast Boy's mentors are also not known. Mal Duncan (who in the comics becomes the superhero Herald) also does not have an official mentor but should if he becomes Herald.
Raven, Starfire, Cyborg, Apache Chief/Long Shadow, Samurai/Wind Dragon, Static/Black Vulcan and El Dorado are rumored to be joining the team. These young heroes are obviously going to need mentors.
Raven - She's a tough one to place but I think Doctor Fate would be her mentor considering they are both incredibly magical in the nature of their powers and Doctor Fate would be able to teach her never to give into the chaos side of her powers. This could also provide plot development for Fate/Nabu by actually having to give a damn about someone other than the entirety of humanity.
Starfire - Another tough one to place considering she doesn't have powers similar to many Leaguers. If I had to choose for her with the current incarnation of the Justice League on Earth-16, I'd say Captain Atom. They both can control solar energy, (the source of Starfire's power) they both can fly and Captain Atom seems to need something making him human, almost like a child. This, however, depletes any hope of Bombshell (Mary Sue Allen) making an appearance but who knows?
Cyborg - Very difficult to place, even more so than the other two. I would toss it up between Green Lantern (John Stewart) and Icon. Both don't have sidekicks, currently. Both would have a fatherly dynamic to Victor. Both could relate with Victor, seeing as how Icon is an alien and John Stewart grew up poor and outcast. It could fun.
Apache Chief/Long Shadow - I would say the Atom but Bumblebee's got him locked down. I might say Hawkwoman, though. Judging by Tye's obvious lack of respect for his elders (just saying. I don't like Maurice either but Tye comes off as not liking authority) Hawkwoman could teach him a few things about manners. She's a tough cookie, a war general from Thanagar and a woman who takes no nonsense.
Samurai/Wind Dragon - Red Tornado. No question. Wind powers. I imagine a scene where the new kids are being assigned mentors and Red Tornado stands up and volunteers for Wind Dragon/Samurai.
El Dorado - I'd say either Black Canary or Plastic Man. Black Canary could teach El Dorado how to control his illusion-based/teleporting powers with bodily control but Plastic Man seems like he could use both a grounding force and a teleporter.
Static/Black Vulcan - Black Lightning. Yeah, no reasoning needed.
Blue Beetle - Green Lantern (Guy Gardner). They both can emit energy from their respective weapons. I'm running thin, currently. So is the Justice League. With one Lantern off world, they need to recruit Guy Gardner. They both seem fun together.
Beast Boy - Blue Devil. Like I said, the JLA needs to get more good heroes in its roster. Blue Devil saved Flash's life. I think that deserves some thanks. Plus, he's just a waste of a good cameo character along with Guy if they don't give him League membership.
Mal Duncan/Herald - Guardian. Guardian would probably asked to join the League again do to the heavy hitters being absent. In the comics, Mal Duncan (after being the Herald), becomes the new Guardian as well. So, naturally, I connect the two.
I think I got everyone. Some partnerships may be flawed but oh well.