Two of the best exterior latex paints are Pratt & Lambert's Accolade and Pittsburgh's Manor Hall. Get an eggshell or satin finish. Never use flat paint outdoors. Expect to pay about $25-$30/gallon for quality paint. And always apply two coats. One coat simply isn't thick enough to last very long. Paint is designed to wear off with time. Two coats cost just a little more in time/effort but can nearly double the life of the paint job.