Young Justice and Green Lantern: The Animated Series will both end when their current seasons, which were interrupted more than once in their runs, end later this spring. Announced through their exclusion on Cartoon Network's "new and returning shows" press release for fall 2013, the series both suffered from broken-up seasons, including a sudden and unexplained pause in the fall of 2012 after only a few episodes of each. A representative from Warner Brothers Animation confirmed to Newsarama the cancelation. Cartoon Network's only official stance is that the new episodes already produced will continue to air.
In their place in the "DC Nation" hour-long block on Cartoon Network will be previously announced series Beware the Batman, which like GL: TAS uses computer-generated animation, and Teen Titans Go, a comedically-bent rehash of the successful Teen Titans animated series, which aired from 2003-2006 (more on both of those below).
Also excluded from the "returning" list, it seems Star Wars: The Clone Wars will be moving to a Disney-owned TV channel, as was expected after their purchase of Lucasfilm. Disney XD seems likely, but no word from their camp yet. Supervising Director Dave Filoni and multiple cast members have confirmed work on a 6th Season of the series. Interestingly, there will be a new LEGO Star Wars special centered on Yoda on Cartoon Network. However, Warner Bros does hold the LEGO license, so this could be a work-around to Lucasfilm's new home (similar to Warner Interactive publishing the upcoming LEGO Marvel Superheroes despite owning DC Comics).
The full Press Release, announced specials featuring Adventure Time, Regular Show, and a CGI revival special of Powerpuff Girls.
Update: GL: TAS showrunner Giancarlo Volpe has also confirmed the end of the series via twitter, stating that luckily they didn't find out via press release. "This time we knew. They just didn't want us to announce it publicly until they did." No comment from YJ's Brandon Vietti yet, though in foreshadowing he announced his and Greg Weisman's work on season 2 was completed way back on October 24, 2012, and he has been working on a Scooby Doo/WWE special for the last six weeks or so, according to his twitter account.