Anime With The Most Interesting/unsual Plot

[Guest monkeyshinobi]

Durarara

Kamisama no Memochou (this is pretty new)

The Melancholy of Haruhi Suzumiya

Fooly Cooly (o.o so short and so weird)

Sayonara Zetsubo Sensei

Higurashi no Naku Koro ni

Bokusatsu Tenshi Dokuro-chan (o.o in english it's killer beating angel dokuro-chan, it's pretty weird)

Death Note

Welcome to the NHK

FMA (interesting plot every anime fan has to see this at least once imo)

Angel Beats

Kanon (2006)

Deadman Wonderland

Katekyo Hitman Reborn

Elfen Lied

Paranoia Agent

Azumanga Daioh (LOL Chiyo's father hahaha)

Lucky Star

[Guest ubjustin]

Death Note

Kaiji

Jojo's Bizarre Adventure 

12 Kingdoms

Vision of Escaflowne (SPOILER: the villain is Isaac Newton!)

I heard Monster is supposed to be great, but I never really got into it

[Guest anmeijo]

mine would probably be...Yume TsukaiWelcome to the NHKAirSolaxxHolicand Clannad.they're all pretty good :]

air and clannad were both really interesting

xxholic too

but i think MIDORI NO HIBI was quite unusual

[Guest nauticalblue]

FLCL and Sayonara Zetsubou Sensei were pretty strange/unusual. I would've said Trapeze, but the plot and themes are far less bizarre than what the animation would suggest.

I thought that the premise and plot of Eden of the East was pretty unique and very interesting as well.

[Guest Autumn1430263885]

haruhi, tatami galaxy, bakemonotagari, arakawa, welcome to NHK, deadman wonderland, Higurashi

[Guest 2partsvodka]

Air

Sola

Ouran High School Host Club

Spirited Away

Howl's Moving Castle (anything Miyazaki is amazingly beautiful with interesting plots)

Death Note

Lovely Complex

Elfen Lied

tsubasa chronicles

Fullmetal Alchemist

Wallflower

Vision of Escaflowne

Dragon Ball Z (I just gotta say, who thinks of a completely different race and have them come to earth? Genius!)

Grave of the Fireflies

[Guest haku98]

ouran high school host club was good - it's actually one of my favorites. 

Spirited away = thumbs up!

...i never really got the melancholy of haruhi suzumiya. I got to watch a couple of episodes but I thought suzumiya was just obnoxious so.. 

[Guest robsta3_stv]

just gonna blow some by you here that i absolutely loved for their great plots. Death Note (youve heard that before). sword art online. theres a span of about five episodes that are terrible but almost the whole series is intense and very interesting. Monster. Terribky scary and very interesting. attack on titan. CRAZY SUSPENSE. THERE IS A GOOD CHANCE YOU WILL WATCH ALL 25 episodes in one sitting. Naruto (groans in the backround) the story actually gets very intereesting once you get to shippuden. 

[bakachin]

Interesting AND unsual plot, huh? there's a lot of interesting animes, i could just list all of my faves, but since the question involves unusual plot too, then it could be any anime that may or may not be my fave (but interesting enough) as long as it has a strange plot.. usually i don't watch animes with unusual plot but some of them are interesting enough to keep me watching till the end..

1. Neon Genesis Evangelion (the original series.. the starting was just like any mecha anime but the ending, well, let's just say it left a scar in my mind)

2. Serial Experiment Lain (the ending took me a while to figure out)

3. NIEA 7 (i don't really get the direction/purpose of the story.. hahahhaa)

well, the other animes i've watched are pretty normal and straight forward, so i don't find them unusual or anything.. so i exclude them from this list..

[maxxima]

Puella Magi Madoka Magica. Starts out your typical cutesy girly mahou shoujo series... and then a major character dies in episode 3. The rest of the series then completely subverts the genre in Faustian parallel. Mind blown.

And of course, Code Geass. Because no one else saw the last episode happening x___x

[Guest Vaaii]

Gurren lagann - The plot and where you think the story goes changes dramitically through out the whole series.

Eureka 7 - Kind of the same as above since it does change substantially as you get deeper.

Kill La Kill - Just ridiculous from the get go if you're into that sort of anime. Think similar feel to FLCL

Madoka Magica - Post before me pretty much summed it up well though.

Onegai Twins - A Romcom with Aliens and some kinda dicey stuff to do with ages. Can't really get into it too much or I'll give away the best of it haha