I swear by the Brooks Brother's non-iron shirts. They're not just wrinkle resistant, your body heat is usally sufficient to straighten out all but the worst creases from the suitcase.

I had a real fight with my mother-in-law over them because she insisted on ironing them and was wearing out the collars and cuffs with the iron.

They start at $88 (replace $ with € for European price. Yes, a rate of 1), but on sale they can be had for under $55, so usually but them in blocks during sales.