I'm in love with piercings and tattoos so any are fine by me. I'm not really a fan of gauges, stretched lips, or toro piecings, but everything else is awesome. My personal favorites on guys are lips rings and eyebrow piercings. It just drives me crazy (in a good way) to see an attractive guy playing with his lip ring with his tongue or fingers while talking to you.
Lip rings and eyebrow piercings on a guy are very attractive to me
I detest eyebrow piercings, I don't really know why but its an instant turn off for me. Tongue and lip piercings are very hot, and I'd be into a nipple piercing as well provided he had the physique to carry it off. I don't have any feeling one way or the other about ear piercings, they are common-ish to the point where I have no negative or positive feelings about them, probably don't even notice with the exception of stretchers. Again, I find stretchers a big turn off.
I assume you mean a belly button piercing? I don't think I could take a guy with a belly button piercing seriously. If you had to go there though you'd definitely need a good physique.