Lynnette from Running With Scissors shows how you can make a side vent for a long top or tunic. The They show it as a variation of their Simple Blouse Pattern, turning the basic blouse into hip length tunic. You can also put side vents at the bottoms of a pair of loose-fitting capri pants or a straight maxi skirt. Go to Running With Scissors for the how-to.
[photo from Running With Scissors]