I might actually be able to narrow it down to one: Gintama.

If I can watch an anime for months on end without getting sick of it and still have it provide me with the same enjoyment as when I first watched it, then it should be safe to say that it is my favorite.

there are way too many lol. i really love gankutsuou and ghost hound though

It's a toss up between Cowboy Bebop and Fullmetal Alchemist (the first version, not Brotherhood). Both have good story lines.

I have a huge list anime that I need to post up that I have seen and enjoyed so much over time it would take so much space. XD I for add in my other ones like X/1999, Tokyo Bablon, Ranman 1/2, .Hack//Sign and a few more XD

My favorite anime are: Berserk, Sailor Moon, Cowboy Bebop, Samurai Champloo, Trigun, Tenchi Muyo, Tenjo Tenge, G Gundam, Gundam 00, Gundam Wing, Vandred 2nd stage.

I don't watch too much anime but I really enjoyed Death Note (It's a classic, I swear!) and Code Geass

Name as many I as I like, em? Beware, it's long! :D

1.) Kodocha
2.) Maid-Sama
3.) Vampire Knight
4.) Chibi Vampire
5.) .Hack//Sign
6.) When the Cicadas Cry
7.) When the Seagulls Cry
8.) Slayers
9.) Ranma 1/2
10.) Tenshi Muyo
11.) Magic Knight Rayearth
12.) Blue Drop
13.) Azumanga Daioh
14.) School Rumble
15.) Full Metal Panic
16.) Ouran High School Host Club
17.) Rozen Maiden
18.) Digimon
19.) Fruits Basket
20.) Princess Resurrection

My favorites are Reborn!, Eyeshield 21, and Gintama. Out of those three, I would say that my favorite is Eyeshield 21. Hiruma is just too funny!

i just finished mushi-shi and i loved it! a bit short for a series though.
and azumanga daioh i havent seen much but its awesome.

Now I have a new semi-love for Panty and Stocking with Garterbelt

@Ashurato - You are officially my favorite person FOREVER.

Gintama is amazing and highly under-appreciated. I have never had another show that had me laughing my ass off and screaming from sheer AWESOME in the same episode. Now if only they'd finish that movie remake of the Benizakura arc so we could get some new episodes again...

Birth (toped my list last week... IT WAS AWESOME)
Rin Daughter of the M,
Gundam all the way to seed. Seed is not liked. From then on it just seemed to die.
Cowboy Beebop
Sailor Moon
Dragon Ball
DBZ
Blue Sub #6
Outlaw star
The first 3 or 4 seasons of Poke'mon
Anything by Clamp and Co.
What newtype usa told me to watch for the most part.
Ai No Kusabi (that count)
Escaflowna
Witch Hunter Robin
Tenchi
Lensmen
Robot Carnival
And so on. (i could not pick I love most anime)

Hmm... listed in no particular order:

Bastard!! (Not the curse word)
Sword of the Stranger
Elfen Lied
Code Geass
Cowboy Bebop
Trigun
Neon Genesis Evangelion
Samurai X
Kite
Kuroshitsuji I & II

I could go on, but I believe that's sufficient for now.

Let's see...

Dragonball Z
Sailor Moon
Tenchi Muyo!
Gundam Wing
G Gundam
Bleach
Kekkaishi
FMA
Ghost in the Shell Stand Alone Complex & SAC 2nd Gig
Azumanga Daioh!
Blood+

And quite a few more :3