My own favorite "wizard" is Ogion the Silent, from Ursula Le Guin's Earthsea books. Or possibly Howl from Howl's Moving Castle, by Diana Wynne Jones, simply because I like him. And after coming up with these two, I think that my favorite wizards are those that have the most personality, whether of the flamboyant sort or its complete opposite.
A wizard who I find somewhat pointless is Dalben, from Lloyd Alexander's Prydain books. All he does is read bits of a book, and throw sticks in front of his pig.
There's a list of wizards in fantasy here on wikipedia, but it seems awfully short...not that I had time to actually study it.
Edited to add: I just saw this picture, concept art from The Voyage of the Dawn Treader movie, over at Fantasy Book Review, and it reminded me of how much I liked that particular wizard! And his ability to mix food and magic.
For some reason, though, I always think of his house as very light and airy, not nearly as dark as this movie version...
And speaking of Howl's Moving Castle, isn't this paper model, from the studio that did the anime version, marvellous? Those who are not as paper challenged as I am might enjoy making their own with the instructions provided.