<mx:LinkButton:id="button" 
        label="WeCodeThings Code Library" 
        click="navigateToURL(new URLRequest('http://www.wecodethings.com/'), '_blank')" />

Here is how to use the LinkButton to move throughout your flex site using a ViewStack:

<mx:LinkButton:id="programmers"
                             label="All Programmers"
                             click="myViewStack.selectedChild=AllPanel;" />

The link button creates a nice button with clean rollover look to it.