Hmm. This is a very interesting thread.
I don't think in words at all. Not in a voice in my head, or seeing the words written out, nothing like that. The only time words come into it is when I deliberately generate them for an imagined dialogue, or something.
My thoughts, well, when I'm really, actively thinking about something, I suppose they're something like 'videos' (I'll play scenarios through my mind) or 'images' (ideas about what something will or does look like, though they're more 3d in that way...). Feelings and sensation may enter into it a little bit, but a lot of my serious thought is future and idea-based, thus neutral and detatched from any sort of here-and-now reality.
But regular thought... well, the vast majority of the time they're just 'ideas', they're 'thoughts', by no means as constrained as a simple film of images or something. They flit and mutate and run amok. I can barely keep track of them. There's not really any way to describe them. They grab ahold of stuff that I see or hear or even think and explode it into a thousand off-shoots of thought, a few of which will be pursued and exploded and so on. :P
So, when I want to put words to something, I often end up speaking in a stream-of-consciousness way, exploring how to put the idea into language through doing so. It just comes out and the words are there to catch it and communicate it. They usually do okay - I'll work around it if there are any difficulties.
The main issue I have when putting ideas into words are when it's more of an opinion, or my assessment of a situation which could either be touchy or something - then my words get stuck. I sometimes really struggle to put across what I mean together with the intention I have. It's easy in my head.
It's funny how a word as simple as 'thought' or 'idea' makes perfect sense to the user, and when we use it, we mean a concept that is really quite complex and difficult to pin down. But there it is, contained in one little word. We tend to forget that our inherant perception of an 'idea' could well be totally and completely alien to the person next to us.