[Boromir88]

Beanamir, good points about Gandalf, and I think he is as close to 'ultimate good' as is possible. As he points out time and time again, he's not doing this for himself, but for Eru and the Valar:

'I am a servant of the Secret Fire...'~The Bridge of Khazad-dum

And his words to Denethor about being 'a steward.'

"Yet the Lord of Gondor is not to be made the tool of other men's purposes, however worthy. And to him there is no purpose higher in the world as it now stands than the good of Gondor; and the rule of Gondor, is mine and no other man's, unless the king should come again."
[...]
"But I will say this the rule of no realm is mine, neither of Gondor, nor any other, great or small. But all worthy things that are in peril as the world now stands, those are my care. And for my part, I shall not wholly fail of my task, though Gondor should perish, if anything else passes through this night that can still grow fair or bear fruit and flower again in days to come. For I am a steward. Did you not know?"~Minas Tirith

Denethor's idea of his 'Stewardship' of Gondor, is a position of Rule. Gondor is his Rule, his command, and no one else's. Then he throws out this little 'well it's mine unless the King comes back.'

But, Gandalf has a very different view of what 'a steward' is to do. A steward is not a position of ruling, but one of caring, and that also makes Gandalf a steward. Gandalf makes clear, as a steward, he rules nothing, but he cares for 'all worthy things that are in peril.'

Gandalf implies time and again, he is not out for himselr (or any ulterior motives as you say) he is a servant, he is a caretaker for the 'higher powers.' It's really interesting how Saruman starts calling Gandalf power hungry:

Saruman’s face grew livid, twisted with rage, and a red light was kindled in his eyes. He laughed wildly. ’Later!’ he cried, and his voice rose to a scream. ’Later! Yes, when you also have the Keys of Barad-dûr itself, I suppose; and the crowns of seven kings, and the rods of the Five Wizards, and have purchased yourself a pair of boots many sizes larger than those that you wear now.~The Voice of Saruman

In Saruman's anger and contempt he makes lofty claims that Gandalf is becoming too power hungry. Gandalf wants power over Sauron (The Keys of Barad-dur) he wants power over the Istari (The Rods of the Five Wizards), and he wants the power of Kings...the power over the people of Middle-earth.

I say this is interesting, because Saruman is making the lofty claims that Gandalf has become power hungry, yet it is Saruman himself who became obsessed with power, and who wanted to 'Rule' over the weak Middle-earthians. We can see exactly how foolish and silly Saruman's claims are because Tolkien ends Saruman's big rant with a silly remark that we all are familiar with:

'have purchased yourself a pair of boots many sizes larger than those that you wear now'

Hmm...strikingly similar to someone saying 'you have become too big for your own boots.'

Saruman makes these lofty claims that Gandalf wants power over everything, but ends with a weak, silly comment, showing that Saruman's rant is simply that...a rant 'full of sound and fury, signifying nothing.'

And after all this I got to thinking, why isn't Gandalf the 'ultimate good.' I mean there doesn't seem to be a blemish on his record, as everything he does is arguably in the name of the 'Valar' and 'Eru.' He is their servant, their steward. I guess it would have to do with something about how when Olorin was chosen as one of Istari to go to Middle-earth, at first he begged not to go, because he feared Sauron's power. That's the only thing I can think of.