The wheelchair salesman from "The Handicap Spot" - "This is like...you're almost glad to be handicapped" and, "I put Stephen Hawking in one of these last week...he's lovin' it."
Philip Baker Hall as Lt. Bookman, the library cop - "I know your type, Seinfeld. Flashy. Makin' the scene. You and your good-time buddies. Well, I got a flash for ya, Joy Boy..."
The doctor who treats Elaine for rabies in "The Glasses": Elaine: I don't need a shot? Doc: No shot. Dogbite. Elaine: No, I know I wasn't shot, do I need a shot? Doc: No shot. Dogbite. Woof-woof. Not bang-bang.
Elaine's friend John-Paul had a few good lines in "The Hot Tub," such as "Why separate knob? Why separate knob?" Then when he's influenced by the way George's Texan buddies speak... "This son of a bitch is ice cold." "Aw, look at the cute little bastard! You're mommy's little bastard, aren't you?" and "Come on you son of a bitch, I'm just trying to be friendly."
There's the old "spectacular" line from "The Implant," but it's been said to death. I like what Sidra (Teri Hatcher) says to Jerry right before she leaves and comes back in: "I think you're both mentally ill."
James Spader in "The Apology," when he snaps and climbs into the ice cream freezer: "I need a drink. Where's that rum raisin...ah here we go, daiquiri ice. What are you lookin' at? Can't you see we're closed? Get out!"
The old guy who played Geoffrey Harharwood (sp?) in "The Gum," when he finds Elaine's button in the lost & found: "Oh my. What a spanking button."
-B.