Here's how to keep the exterior paint from peeling off your house, if you live in a damp climate. Using a breathable oil primer will allow moisture buildup from inside the house to escape. Cover the primer with two coats of 100% acrylic latex paint. All climates are prone to mildew, and latex paint is inherently resistant to mildew.
For more on exterior painting, consider:
Exterior Paint 101
Weatherproof with Paint
How To: Avoid Painting Problems