Obviously the half second flash of Leonard in the mental hospital.
When "Sammy's" wife is trying to get him to remember things, and gets terribly upset with him when he doesn't, while she is crying into his shoulder she mutters "Leonard" instead of "Sammy".
Last one is pretty obscure but interesting...
When Leonard is talking to Natalie in the restaurant and recalling what he remembers about his wife, there is a shot of her (from the floor up) lying down with her head slightly off the side of the bed (or couch) with her eyes closed. She blinks a couple of times and then her eyes stay open.
Could this be Leonard's wife going into her insulin-induced coma?
(It has also been suggested that this shot is in reverse- which means her eyes would be open at first, blink and then close)
Interestingly this shot is also when Leonard says "And how much you hate the person who took them away." Is he subconsciously referring to himself?
Personally I think Teddy was telling the truth at the end of the film.