One of the most basic and easily overlooked effects in Adobe Illustrator is the arrowhead effect. You may not need an arrow everyday, but when you do you will be happy you read this.

Use the pen tool or line segment tool to draw a line. Go to Effect > Stylize > Add Arrowheads... Next choose your start and end style using the popup menu. This is one simple feature that is great for graphs, lists, buttons etc.