Well, another way to do this is look at the Japanese animated media brands that have majorly appealed to kids in the West and start looking at when they were created:
1979: Gundam
1984: Transformers
1985: Dragon Ball
1986: Saint Seiya (more so Europe)
1991: Sailor Moon, Sonic The Hedgehog
1996: Pokemon, Yu-Gi-Oh
1997: Naruto, Digimon, One Piece (mostly Europe)
1999: Beyblade
I think the closest thing to a recent show would be Bakugan in 2007, which I don't believe is actually anywhere near as popular compared to the others.
Is there something recent I'm forgetting?
If we're talking about aiming to sell something like 200-300K in the West then the comparison is of course very different, but I'm assuming we're talking more about major brands.