The messy look is in style today, even for a formal occasion such as the wedding.  Paris Hilton gives a great example of a very simple wedding hair style that is both clean looking and slightly messy at the same time.

Extra height is created in the crown area and the hair is pulled back into a very high ponytail.  You may want to run a flat iron over all the hair before you do this, especially if you have frizzy hair.

Wispy bangs are left out and softly drape across the forehead from a deep side part.

Imagine this style with a fancy hairpiece pinned at the back near the ponytail. 

See messy style, left, for example of a real mess that looks actually pretty good. Creating the messy look is an art in and of itself.  It requires certain skills and techniques to create just the right mess.

Notice how the hair is pinned back in the front area, see below, using decorative clips.  If you do not have this much hair, there are even clip-in hairpieces that can be used to create this look.