Not that this point has not already been talked to death, but last night's rerun has yet another piece of evidence that Kramer is the character's last name. (I can't believe anyone would actually think it was supposed to be his first name) When he goes to the will-call window at the football the game, he asks for a ticket for "Kramer". The ticket guy holds up an envelope with "Mr. Kramer" hand written on it. He won't give Kramer the ticket without ID.
Now, if you were leaving a ticket for someone at a box office, they would ask for the person's last name. They wouldn't want the first name without the last. And even if you believe that Kramer is the first name AND Joel Rifkin had given it to the box office AND the ticket guy had mistakenly written "Mr. Kramer" because he thought it was a last name, why would asking for ID matter? The irony of this scene is that if he had brought his wallet, his ID would match the name on the ticket and he would get in. But he didn't, so it doesn't, so he doesn't.
This, along with "Babs Kramer", "Isosceles Keamer", and the name on the screenplay, should be the final nail in the coffin of the "kramer's his first name" argument.
Thanks for your support.