Yes, I consider myself straight but naked guys turn me on more than naked women. Here's my theory, and this is a case in which I'm probably over-analyzing something that really should just be accepted for its simplicity (the simplicity of a very basic human urge): If you don't consider women's breasts a sex organ (they weren't made for reproducing), then women don't really have (easily) visible sex organs. It's easier to see a guy's full sex organ at a glance - penises are always fully visible as an external body part. And a man's sex organ is, in a way, meant to be visible - it gets bigger and showier to demonstrate that the man is ready for sex. When a woman is sexually aroused - when she's physically ready for intercourse - she doesn't show it anywhere nearly as clearly as a man. I'm very visually oriented (and I think men generally are), so men's bodies as something more visual and showy are going to appeal more to men, I think.
Of course I'm turned on by seeing an erect penis - a man who's in a state of sexual arousal. But I'm also turned on by seeing a flaccid penis - just a naked man who's not ready for sex. I guess I find this latter state of a man appealing too because of the taboo of nudity - that it's supposed to be bad, something hidden and something we're not supposed to see. What turns me on about a flaccid penis is knowing that it's something private, something usually reserved for that man's partner only. I get turned on by seeing a man take his dick out in a public bathroom because I know it's used for one function - peeing - but I sort of secretly think in my mind that it's used for another more pleasurable function (sex).