The really old ones have to do with "Haven't we met before", and "Do you have the time".
An all time classic is "Can I buy you a drink" (which if used had better be supported with the ability and intent to buy said drink...)
Joey (from Friends) seemed to knock any woman with "Hey, how are you doing", but i guess that only worked for him.you?"
Good luck...
Or you could use the direct approach, "Hi, I saw you across the room and I think you're great. Mind if I join