Hi Luke,
When it comes to God, I can doubt in many different ways:
1. doubt that he exists (Heb 11:6, Psalm 14:1, both deal with this space)
2. doubt that he is who he says he is (Ps 78:7-9)
3. doubt that he tells the truth and/or keeps his promises (Heb 11:6, 10:23
4. doubt that he will give me wisdom when i ask (James 1)
5. doubt that he can help me (couldn't be bothered thinking up more quotes)
6. etc
It's probably relatively important not to conflate all of these, lumping all doubt into one simple category and painting a big red X on the box

James 1 is very specific (dealing with asking for wisdom), and Heb 11:6 is as close to a statement of the obvious as it gets, suggesting that those who come to God should probably believe he exists
Then there's the issue of quantity. Faith is not on or off, it comes on a continuum. Jesus talked about faith "as a grain of mustard seed", which would be meaningless if you couldn't have faith of say, a mango seed. The disciples asked Jesus to "increase their faith", and in Mark 9 you've already mentioned a fella who confessed to having belief and unbelief simultaneously, but wasn't told to come back when he could leave out the second bit.
I don't reckon Otberg makes much sense. He says that where certainty is faith isn't, and that sounds a wee bit like rubbish. It's true to say that faith can be where certainty isn't (Grace's post made that point beautifully - and certain passages of Lamentations and Job come to mind, did Daniel know that God would answer his prayer? probably not, but he definitely trusted God), but it's not true to say that certainty means there is no faith. I just think there's no relationship between the two - they're on different scales.
I don't reckon i've made much sense either. Can you pick through that and find something useful? If not i'll try again...