Okay, so I have been able to find a definitive answer!
 
> Naruto Narutimate Hero 3: Finally a Clash! Jonin VS Genin!! Indescriminate Gran
d Melee Tournament Meeting!!

is the longest titled anime with a large 107 characters or 87 characters without non-alphanumeric characters

Second Place goes to:
> Digimon Adventure 02: Zenpen Digimon Hurricane Jouriku!! - Kouhen Chouzetsu Shinka!! Ougon no Digimental

With 104 characters, 85 alphanumeric

And Third,

> Dragon Ball Z Special: Tatta Hitori no Saishuu Kessen - Freezer ni Idonda Z Sens
hi Son Gokuu no Chichi

102 characters, 82 without.

I discovered this by writing a small Python script to iterate through a dump of AniDB's database of anime titles and check each one, [which you can find on their site][1]

If anyone is interested, you can find the script here: https://gist.github.com/ianfhunter/43599d30384b9b7aa0c6 (but I only hacked it up in 5 minutes, so it's nothing special)


(The shortest is C)

  [1]: http://wiki.anidb.net/w/API