Eyecatch

An eyecatcher is a scene or illustration used to begin and end a commercial break in a TV program, especially in anime and tokusatsu shows.

Each Yu-Gi-Oh! anime series has a different kind of eyecatchers.

Yu-Gi-Oh! (second series anime)
The second anime series' eyecatcher shows the Millennium Puzzle spinning with Egyptian hieroglyphic in the background.

Yu-Gi-Oh! GX
Yu-Gi-Oh! GX has two different sets of eyecatchers; all of them show the characters who were most relevant in the episode, usually the characters who Duel in it, sometimes with their main monster shown in the background. In the beginning, the first eyecatcher showed one character, and the second, the other. Later, starting on season 3, the first eyecatcher was skipped, with the second showing both characters (more than 2 sometimes).

Yu-Gi-Oh! 5D's
Yu-Gi-Oh! 5D's too have 2 different sets of eyecatchers, although they didn't change from episode to episode. The first set was used for seasons 1 and 2, and showed Yusei with "Junk Warrior" (the first one in a Ground Duel and the second one in a Turbo Duel). The second set was used from season 3 to 5, and showed two shots of Yusei with "Stardust Dragon".

Yu-Gi-Oh! ZEXAL
Yu-Gi-Oh! ZEXAL doesn't have an eyecatcher animation. Instead, its logo is shown in the down left corner for both the begin and end of the commercial break. The same goes for Yu-Gi-Oh! ZEXAL II.