Nah Lehmann is past it imo. he was a good keeper though.
Cech is probably the best but if Given was with a top team, he would be considered among the best in the World. I have only seen him make one bad mistake (the one where the striker came around the back of him, took the ball of him and scored). Some of the saves he makes are superb.
Buffon, Casillas, Cech, Kahn, Van Der Sar, Julio Cesar, Coupet, Canizares, Given are my top keepers in the World.
Oh and Brad Friedel is a great keeper as well.