=====> Lightning component <======

<aura:component implements="force:appHostable">
           <ui:button press="{!c.navigateIt}"  label="Go!" />
</aura:component>

======> Lightning Component Controller <======

var navigateIt : function(component,helper,event)
{
        var navigate = $A.get("e.force:navigateToURL");
        navigate.setParams({ "url" : http://www.google.com"});
        navigate.fire();
}