During Ned's dream sequence, for a single frame, a blank cell with a cross through it can be seen. This is a misplaced blank animation cell.
When the Simpsons and the Flanderses are all in the car, Rod appears to be missing.
When Homer and Ned are talking to Springfield QB Stan Taylor, you can see that the number 10, to mark the 10 yard line, has been reversed on the playing field to read 01.
When Homer is throwing out his and Marge's wedding picture you can see in the picture Marge is not pregnant (or at least not showing). Homer and Marge got married when she was 8 or 9 months pregnant.