Hozuki no Reitetsu should have another season, and I don't see why it shouldn't.
There are a lot more characters that have yet to be animated, and there's apparently an allusion to Greek mythology! Comedy/episodic anime seems to be easier to work with so hopefully this wish will come true.
I know it is already confirmed but I’m so glad that Kuroko no Basket is getting a third season. KnB totally deserves to have another season and I can’t wait for it!
To be honest, after how awesome season 1 was I thought a second season was going to be automatic but I guess not. It both needs and deserves a season 2 though. It also always seemed like a series with a lot more story to tell and adventures to be had.
No Game No Life
One of the best, surprise, series all year! It's even got an ending that implies a renewal... they aren't going to make us wait till next year are they?
Valvrave the Liberator (fall 2013)
Obviously because damn plot hole, rushed ending. Altough it seem already turned into sh*t before the ending, at least season 3 can fix it, or I hope so
Gekkan Shoujo Nozaki-kun
I had a lot of fun watching this anime. It was different from your typical romance anime. It was funny and cute and there were moments in the series that reminded me of Ouran High School Host Club very much. I really hope there is another season of GSN, I would love to see more of Chiyo, Nozaki, Mikorin and the rest of the gang.
Probably echoing a lot of similar thoughts others are having, but it would be awesome and logical if there was a third To Aru Majutsu no Index season. It may even be in the works by now, I'm not sure. But there's already so much material in the light novels to work with and the whole franchise itself is pretty popular. Hopefully with To Aru Kagaku having finished its 2nd season a while ago, now JC Staff will have the next installment of Majutsu in the works.
I have to many in my list but here's some.
Katekyo Hitman Reborn
High School of the Dead
Would like this anime to extend past the temple mission and cover Izumi/Vampires as well as Osaka arcs.
Sket Dance I love that series, and it had 77 episodes so I'm happy but, It didn't complete the manga, and I tried to switch from the anime to the manga, but the humor doesn't translate well IMO. I would love for them to have a second anime.
Attack on Titan
Claymore, yes. Finish the entire story