Not sure whether to include T.H. White’s Merlin. He’s not exactly crazy, after all.
5. Fizban the Fabulous (Margaret Weis and Tracy Hickman) (except he was kind of faking)
4. Master Elodin (Patrick Rothfuss)
3. Arisilde Damal (Martha Wells)
2. Adept Havelock (Stephen R. Donaldson)
1. Antryg Windrose (Barbara Hambly)
Anybody else I should have on here?
Edited to add: I forgot Vic! Put in another entry on this list:
6. Vincianus Polymage (Greg Costikyan)
…from the unfinished “Cups & Sorcery” trilogy.
Matthew Elmslie 
I’ve been looking for some good fantasy novels to read and I’d be very interested in reading about crazy wizards. Thanks for the recommendations.
Oh, well, I suppose I should have included titles, then; sorry ’bout that. Respectively, the names of the relevant series (or the specific novel, in the case of 3.)) are:
5. Dragonlance Chronicles
4. The Kingkiller Chronicles
3. The Fall of the Necromancer; The Fall of Ile-Rien
2. Mordant’s Need
1. The Windrose Chronicles
Also you should know that these crazy wizards are usually not the main characters of the books. Enjoy!