Hm.. I think with proper styling, guys can pull off nearly any look and make me look twice. But for personal styles that make me take notice include fitted shirts, tailored trousers, or dress shirts for nights out; for casual, jeans are fine as long as they're by the waist and hiding your drawers. I'll admit, I'm a sucker for a shirt that accentuates arm, shoulder or back muscles if they guy is toned. Classic colors, neutrals with pops of color that say that a person is calm and grounded, but not dull. Waistcoats/vests can look nice and can be dressed down as well.
Overall it depends on the individual though. For example, my partner looks excellent in dark colors, and a punk/rocker style like dark clean denims and black muscle shirts with a slightly military style coat. My friend however would never be able to pull that off, and looks a world better in lighter colors, and a more prep style.
Things I avoid? Hm... Overly baggy or 'sagging' pants. I don't care how much air someone needs down there, I don't need to see it hanging out the back.