Im going to be wearing a navy blazer & gray slacks to a wedding in Italy this September. I would love to know what color shirt and tie you recommend me to wear?
White shirt. It's a wedding. I always cringe when I see gaudy colored shirts at otherwise formal events -- more so than when I see them normally. Even if the affair is relatively casual (for some reason), white is always a good choice.
The tie choice would, I expect, be more dependent on the type of people whose wedding it is and the environment that they've cultivated with their planning choices. If they're trying to make it a "fun" wedding, you'll stand out more with the classic look. Generally that's a good thing -- because it's a good look -- but I've always thought it's appropriate at weddings to blend in so as to not distract from the bride and groom. It is, after all, their day.
If you must go with a colored shirt, I'd say a navy bengal stripe button collar is a good choice. Second to white. But in that case: solid tie.
@Scotty13 Well, with the grey pants, it seems that you're setting yourself up for a pretty traditional look where the white and burgundy suggested earlier fits perfectly. Maybe others have a different opinion. Are light tan (Stone or a few shades darker) out? It seems that would set you up for more "fun" tie choices. Solid (textured), though, with the bengal stripe. It just seems to me that putting a "fun" tie with an otherwise traditional set-up doesn't work.
^^ This. A lot, this.
I don't think there is anything wrong with a clean, conservative look being inappropriate for a "fun" wedding -- unless you're a dud and want to *look* fun while being so. Then again, I've gotten used to and feel comfortable with looking "overdressed." What Michael suggested looks sharp. If you've got a problem with that conservative look, the bengal stripe with a solid/texture orange, coral, purple, yellow tie would be fine -- whichever is most flattering for you considering your potential radiation/face tattoo/Susan G. Komen status. I only say those because I've always liked orange, purple, and yellow with navy.