Since it's debut in March, Green Lantern: The Animated Series has built an incredible fanbase from both comic and non-comic fans alike. The series is to return in September alongside Young Justice in the DC Nation programming block. Last season's finale saw Team Interceptor dealing with a Red Lantern army who found their way through the Maelstrom to attack Oa. In the images below, you can see Peter Markowski's concepts for the Lighthouse and The Maelstrom.
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You can see some more pieces at his blog.
Meanwhile, Zak Plucinski has released his intial designs for Tomar-Re and B'dge, who was later finalized into Ch'p. You can see both characters in action by watching the Comic-Con sizzle reel for Season 2.
Producer Giancarlo Volpe (who I'll be interviewing soon) has posted this collage on his Tumblr. These are color keys from several episodes created by all of the artists involved in Green Lantern: The Animated Series. Let's ask Giancarlo to release each art piece individually in high-res! They'd make for great wallpapers, don't you think?