Highsc...boobs of the Dead
One by one, the superbly placed fan service just takes my breath away. The main characters' teamwork is also amazing. Excellent main protagonist, does what needs to be done in a careful manner without overthinking it.
Fullmetal Alchemist: Brotherhood
Others say the first adaptation was better. Definitely not true. Brotherhood is definitely better. So much of the plot made more sense and the important back stories were revealed. In this "true" adaptation, the story was grander and more complicated.
Gundam 00
Awesome back stories, awesome battle scenes, awesome plot, awesome landscapes, awesome war, awesome pilots, awesome tactics, awesome girls, awesome... awesome...
Code Geass
Death Note tactics combined with mecha. Makes you have headaches at night. Then you'll dream of the MC's red eye. That's how good it is. Full of surprises too. Ones you've never even had a glimpse of in other anime. This is also one of the very few that made me tear up.
To Aru Majutsu no Index, To Aru Kagaku no Railgun
The characters and concepts are so unique, you never would have thought someone would come up with such a number of interesting aspects and put it into one fantastic story. Railgun is a spin-off of Index, but it has a lot of plot to offer. Most of my female friends prefer Railgun than Index.
Tales of the Abyss
Beautiful scenery and nicely designed characters! They're actually from a game, so it makes sense. The series is an adventure and it makes you feel like you're playing an adventure role-playing game. Also has the greatest character development I've seen, that not even Kenichi, the greatest disciple can beat. The MC came from annoying little son of a prick to a real, amazing hero.
The Tower of Druaga: The Sword of Uruk + The Aegis of Uruk
Another game adaptation... I think. It's basically a dungeon crawler adventure anime. It has a very good plot and breath-taking battle scenes. The mystery also kept me wanting more until the very last episode of Aegis.
Zero no Tsukaima
The concept behind the powers of the main characters got me hooked and nicely placed fan service left me asking for more. The steadily moving plot also kept me from getting bored.
Strike Witches 1 and 2
Air force/military combined with girls with tails and animal ears. They're basically girls with guns that fly. Good enough plot, good enough concept... err, fine, I know! I'm biased because I like aerial combat and cuties! That's also why I liked Infinite Stratos (IS), but fine, I won't include that in the list.
Sekirei
Interesting plot, interesting set of characters but lousy main character. Pfft, fine! I'm biased again because I like... oppai!! Oppai banzai!
Gurren Lagann
My drill will pierce the heavens! Who would've thought there was such an in-depth meaning to his drill? Quite a good concept.
Claymore
Damn good battle scenes! I wish they would continue the series in the future. A few years have gone by, though. There's little hope. It's still worth your time even if the story wasn't finished in the anime.
Angel Beats!
The plot is so abstract and tragic and yet it's so good. It made my heart hurt so much that I deleted it accidentally! Holy crap, give it back...
As for the recent ones...
Fractale
Way too beautiful to be just a series. I thought I was watching a movie! Has a nice mystery to it too.
Denpa Onna to Seishun Otoko
Every one of the girls are wonderful in their own way. Erio, the quiet one, is retardedly cute. Ryuushi [RyuuKO!] is energetic and adorable. Maekawa stuns you with her logic, usually because it's either a very wise or a very twisted one. Meme is the main contributor of comedy, and I find her mature charm likable too. Also, if you're the type to dig deeper, actually you can, and there's a concept that the story revolves around -- hope.
Kore wa Zombie Desu ka?
Another anime with a wonderful female cast. Hilarious scenes and good enough plot. No need for additional build-up, the first episode will get you addicted, I guarantee it. So watch. Now. Arguably the best series among the ones in its season.
As for the on-going ones, I think it's too early to tell if I declare them one of my favorites, but I'm watching these closely:
Nurarihyon no Mago Sennen Makyou
Ao no Exorcist
Beelzebub
Dantalian no Shoka
Mayo Chiki!
No. 6
