Young Justice.
Cancelled right when villainous plots were beginning to unravel/be revealed...
I am so pissed about that. It's the first show in years that I've actually wanted to watch. I don't suppose you know why the show kept having its time slots moved around so much? First it was Friday primetime, then Saturday mornings, couple of hiatuses (including that really awkward one in the middle of S2), then boom, done. Not enough viewers. Yeah, mystery how that happened.
Gods, I hate how a show with actual plot and depth got screwed over so badly. Oh well, looks like I'll be picking up the series on DVD when I find it (same with the comics).
Also not happy about Tron: Legacy and Green Lantern TAS getting the axe. Not a fan of GL's animation, but they both had some good story arcs.
Also, I don't know if this counts as spam or what have you, but I've come across a site recently that's trying to revive lost TV series. The idea is to have users submit shows they want to see revived. Once the show has been given enough support, SMGO's creators will approach the necessary studios to discuss bringing the shows back to life. Funding for bringing a show back will be generated through crowd funding; if enough revenue is generated by a certain deadline, production will begin and the revived series will be streamed through SMGO's website. Profits will be generated by subscriber fees, as well as ads played for those who prefer to watch for free. And yes, I realize the web site is somewhat sparse right now. According to the FAQ section of the site, it was prematurely discovered about a month ago, and the support is has received has caused SMGO's creators to push forward their deadlines, and try to get their project up and running ASAP (they've already begun discussions with various studios about the viability of this project, and seem to be getting positive feedback).
So, if anyone wants to try something new, and attempt to bring some of these beloved series back to life, feel free to give it a go.
http://www.smgo.tv/https://www.facebook.com/smgotv?fref=ts