What kinds of book covers attract your attention?

Well, it depends. I have different preferences for fanfic/FP/online fiction than I do for published novels. I'll just talk about published because I think that's what you mean.
I'm a sucker for pretty fonts. If you have like a Comic Sans title font, I will seriously put your book down and leave the room so I don't have to look at such a travesty. Also, I like seeing nice watercolors on a cover--those are always spectacular. The one thing that really bugs me is, being a huge m/m fiction reader I encounter this a lot, there's always half naked people on the cover of things I want to read. Why do publishers think this is what I want. Naked people are nice to look at, but not nice to have on book covers. It looks kind of cheap and it doesn't draw my eye. They don't even need people on the cover! I'd settle for a nice illustration or graphic design.