Photoshop :: Choosing Font/Typography

How do you choose fonts to go with various images? Do you just cycle through the ones you got until you find what looks right? Or for certain things do you generally use a set of fonts, like this font that font and another font to use usually when making an ad (or go more specifically? and go for ceratin fonts when the subject matter is cars, as opposed to nature, as opposed to computers, as opposed to people etc.). Are there guides to choosing fonts that I just can't find? General fonts used with fantasy artwork, general fonts used with sci-fi artwork, fonts used with something else more broad or more specific?

And how would a knowledge of typography help exactly with choosing fonts, or would it help?

I'm just asking this out of pure curiosity, sort of... And the fact that I'm not too fond of trying to pick out fonts for an image/sig/something by having to cycle through all of the fonts that I have. I'm just wonderin' if, when I'm working on something more on the fantasy side, a certain group of fonts generally look better, or when with something else, another set of fonts generally look better.