I find Noir and Now and then here and there to be the best animes ever (except for Rurouni Kenshin that is).

Now and then here and there is only 13 eps, but a lot happens in this anime and you will not be disapointed if you like the anime where the whole world around you is gloomy.

Noir is 26 eps. If you like killing merged with cleaness, this is your anime. There si no blood at all throughout the whole anime. It's about two girls (well one of them is like 14 years old and the other more like 20) who tries to find out about the younger girls past while they take various missions as assassins. The further into this girls they get, the more dangerous their world become, it will also become depressing the further they get. Watch this anime.

Apart from that i'd also have to say that one series you just have to see is the Seikai series witch consists of Seikai no Monshou, Seikai no Senki and Seikai no Senki II a.k.a Crest of the Stars, Banner of the Stars and Banner of the Stars II...

This series is great.