The old Nautilus pullover machine might be the best overall lat movement that exists.
But if you don't have access to antique strength training equipment, then the dumbbell pullover is a solid alternative. Problem is, once the dumbbell crosses over your face there's basically zero resistance in the movement. Here's how to solve that problem.
Dumbbell Pullover With Band
Adding a band increases the resistance through the movement. You'll get a similar affect as you would with the classic pullover machine.
Finally, some ammo to use against those putzes who insist on benching with their feet in the air. Craig also makes the case that chin-ups are a better lat exercise than pull-ups. Let the arguments begin!