Mirai Nikki is the best anime i have watched. What's your favorite Anime/Manga?

Azumanga Daioh

Serial Experiment Lain still takes the #1 spot for me.

Meh, i just stick with the old, i have yet to watch many animes that had such an emotional impact:

Evangelion

FullMetal Alchemist (Brotherhood)

Akira (not a series in know)

As for classics:

BT-X

Ranma 1 1/2

Saint Seya

Conan Detective

Anime - Monster.
Manga - Claymore.

New Anime: Baccano and Durarara

Manga: Hellsing and Gantz

Dont want to name any classic here, too much awesomeness.

Code Geass FTW! Also HSoTD.

Gasai Yuno was kinda scary :p But I still like the anime overall :)

Favourite anime -> Toradora!, Angel Beats, Another, Zero no Tsukaima and etc.

Hunter x Hunter and Eyeshield 21 :)

I did enjoy Mirai Nikki, but it certainly wasn't my favourite. The main character didn't learn anything out of all he did, and at some point it gets pretty repetitive and much less realistic than the first 6-7 episodes. If you liked it, Deadman Wonderland might be up your tastes. And Shiki too.

In the genre, I did prefer Umineko no Naku Koro ni, and its older brother Higurashi no Naku Koro ni. Both take the murder/mystery genre to a level unequalled by any other anime I've watched.

I've stopped watching the more recent series, since they're all relatively average. I did see an episode of Mirai Nikki on TV while I was in Japan and it looked intriguing though - might need to look into it. As for my favourites, it's probably quicker to look at my vote list:
AniDB Vote List

Boku no Pico

I'm going to be obvious and say Fullmetal Alchemist (manga/Brotherhood). I've been enjoying the manga of Spica & Wolf and The Melancholy of Haruhi Suzumiya, too.

Clannad for sure.

anime --> serial experiments lain, rahxephon, texhnolyze
manga --> blame!, hommunculus, dragon head

kiss x sis?

Steins;Gate, Rainbow and Detroit Metal City!

Haven't watched that much yet, but for me it would be Code Geass ;)

chaos;head...really interesting anime

Neon Genesis Evangelion, Macross, Macross Frontier. Old anime are pretty awesome...

Gundam everything

REBORN, NARUTO, GUILTY CROWN, ACCEL WORLD,

Beck (Mongolian Chop Squad), Clannad and Steins;Gate.

Ghost in the Shell - Stand Alone Complex

It's also a damned shame, Tokko didn't get it's second "season". Dat cliffhanger. (Rokujo + Suzuka wwubwubwub)

Yu-Gi-Oh.

Initial D