One ESPN commercial about Shaquille O'Neal and Scrabble premiered when he was playing for the Phoenix Suns, in 2008. In October 2009, after he had signed with the Cleveland Cavaliers, this commercial aired. The videos are filled with other gags if you notice them, such as different analysts in the commercials suggest that he plays Scrabble the same every game.
In a Swedish women's magazine, there was an ad for "Mini-baguettes", bauettes you baked in the oven. It said: "If you put six mini-baguettes in the oven now..." About ten pages later, there was another ad for them, saying "...they'll be done by now."
Then of course there's the old Energizer battery commercials, which would start out with an actual commercial for the brand, then cut to a (fake) second commercial for something completely unrelated. Halfway through the second commercial, the Energizer Bunny would appear, moving across the bottom of the screen, and the Energizer commercial's announcer would say, "Still going. Nothing outlasts the Energizer."
There was a car advert in the UK in which the car jumped over the advert break. At the start of the adverts you saw the car go up a ramp; then the rest of the adverts followed; then the car landed again after you'd forgotten about it.
Recently in the U.S., AT&T aired a commercial for a phone service that had the announcer start flipping postcards of places their service covers onto a map of the continental United States. The commercial fades away. Two or three commercials later, there's the announcer again, still flipping postcards, only now the map is nearly completely covered.
In May 2011, there were ads all over with only one word on them, "Tomorrow". Cut to a week later, where all the posters have been replaced with "Tomorrow is today. - TNT Postal Services".