As you'll might have heard the big news, that Beast Boy, aka Garfield Logan, will be joining the cast. He’ll be voiced by actor Logan Grove. And also another female character added to the show by the end of the season to join Artemis and Miss Martian.  Wonder Girl? A New character? The source wouldn’t confirm.   
Could it be Wonder Girl, Zaatanna or Raven? 
There were legal issues surrounding Wonder Girl, but not any more. according the Producer Greg Weisman’s blog: “There is NO LONGER a legal issue about Wonder Girl. But there was when we originally developed the series.”  Maybe Wonder Girl won't be on the first season, but will join in the second season if they have already produced the episodes of the first season. And Zatanna might join in the first season. Beast boy might just make an appearance mostly for one episode, as his voice actor, Logan Grove is a 10 years old.  So Garfield Logan aka Beast Boy being 9-10 year old, might not have powers yet or be part of Doom Patrol. There is a very slim chance of his joining the YJ. 

i hope it is Wondergirl. That would be awesome

As a big fan of Beast Boy, I'm not too excited about him being brought onto this show.  It's a great series, but considering the kid they have voicing him looks 10 or 11, I imagine he will be showing up for a "babysitting" episode and maybe make a few guest appeances after that.  I'd rather they not use him at all if they are just going to do that with him.
 
As for the new female teammates.  Wonder Girl would make sense, but I do think there is some leagal red tape preventing that.  I also don't think Raven needs to be involved at all.  They are too busy with "The Light" to need to involve Trigon in the mix.  Artemis fills both the roles that Speedy or Raveger could do, so I doubt we'll have them either.
 
I imagine that the most likely choice is also one of the less obvious options.  I imagine the new female teammate will be Zatanna.  I feel this is what they have planned as it seems like the only reason why they made the first Zatarra part of the League and not her, even tho she is far better known.  A few little tweaks to the continuity (which they have already done for the likes of Dick, Wally and the new Aqualad) and Zatanna is now young enough to be on the team working as Zatarra's sidekick. 

I this it's Wonder Girl. I remember hearing them they resolved the red tape and would add Wonder Girl later in the season.

" I tought they couldn't get Wondergirl because of liecensing. "

" I tought they couldn't get Wondergirl because of liecensing. "

Why is this in Batman forum?
 
Anyway I'd like to see Raven or Zatanna.

There legal issues surrounding Wonder Girl, but not any more. From Producer Greg Weisman’s blog: “There is NO LONGER a legal issue about Wonder Girl. But there was when we originally developed the series.”  Maybe Wonder Girl won't be on the first season, but will join in the second season if the had produced the episodes of the first season. It could be Zatanna. Beast boy might just make an appearance for one episode, as the voice actor is a 10 year old.

Donna

I hope Beast Boy remains a guest star, maybe along with the Doom Patrol.

I'd like to see wonder girl(donna troy). Robin needs a female counterpart. She doesn't have to be a love interest but the brother/sister chemistry is all there,a strictly platonic relationship. If you're asking me which character I'd be interested in seeing join the show then I have to go with Nightwing. How cool would it be to see a time-skip? He'd still be too young, I know..maybe season 3 though :)

Yeah, I'm not really a Best Boy fan so I would have preferred a different character joining, but I'll wait to see how it turns out until I knock the move too much.
 
The two I'd like to see would be Wonder Girl (Donna) and Raven. That way the numbers would be even with four boys and four girls, and it would give you a pretty interesting and diverse set of personalities and abilities.

 I kind of think that they're going to have Superboy and Miss Martian finally start dating then have Cassie on the show and do the whole love triangle thing...I personally want Slobo

Star Fire, Raven, Cyborg.

" @cattlebattle: But...she too old. "

How about Secret?

Starfire, Raven and Beast Boy.

I think Wonder Girl would be great in the series. I mean she hasn't really made any appearances on TV.

"I think Wonder Girl would be great in the series. I mean she hasn't really made any appearances on TV. "

Definitely Cassie, although I am curious where things are going to go with Miss Martian and Superboy. But Wonder Girl definitely needs to be in this series.

I would like to see Raven and Beast boy...

But with Raven, as some one already pointed out, there would be the whole Trigon thing and well that was already done in Teen Titans.
And a Teenage Zatanna would be kinda weird seeing as she's usually (I'm guessing) in her late 20's early 30's. Using Zach would make more sense. (If they wanted some one of the Zatara family)

And WG/Donna might actually work. If the legal stuff has been sorted out.

They must get rid of Artemis and return Roy to the team.
And Miss Martian must die (I hate her more and more with every "Hello Megan"!).

I hope it's Cyborg =).

I'm betting on Wonder girl, since this  team is made up of Sidekicks of JL members. Raven would be fun and a good exception to the rule.

If its Wonder Girl, it has to be Donna.

Beast boy has been confirmed, they already got a vocie actor for him

ZATANNA or WONDERGIRL (Cassie or Donna i don't care)

I think the Wonder Twins should make an appearance since we haven't seen them in a very long time. They did show up in the Young Justice comic so its a possibility that they could show up. Wonder Girl would be my best guess between her, Zatanna, and Raven but Zatanna's father may die so she could take his place. I'm a huge fan of Beast Boy and I'd love to see him go all beasty on everybody and join Young Justice.

Let em stick with the peeps they have