Gintama's filler is excellent, mainly as the episodic and humorous nature of the series makes it hard to tell what is and isn't filler unless reading the manga's entirety. Some of my favourite episodes of the anime are filler ones, in fact.
Other good filler include:
- Asgard Arc of Saint Seiya. It's not exactly outstanding, though it at least offers some things the manga canon never did, such as making the God Warriors more fleshed out villains than most of the Marina Generals or Spectres that succeeded them as the henchmen villains of later arcs.
- Atlantis Arc of Yu-Gi-Oh! Not much of a change from the quality of the series, though it contained some good duelling strategies, at least until the PIS at the end of the arc.
- Filler in City Hunter. Like Gintama, it has an episodic nature, so filler isn't much of a divergence in quality.
- Many of the filler scenes in Hokuto no Ken that make Kenshiro even more badass, such as Kenshiro destroying a tank and Kenshiro VS Glenn.
- The post-Four Beast section of Toriko's anime. This was one of the few good things from the Toriko anime, since it offered a plausible and more exciting version of Toriko testing his new power than the manga did.