theyre both Schinchiro Watanabe projects, so just look for his work.KefkaCultist said:Check out Samurai Champloo. It's somewhat similar to the style of Bebop and not childish.
EDIT: And before you get turned off by the hip-hop theme of it: I abhor hip-hop and rap stuff, but the anime is done really well to the point that I actually like it.
if you like animated shorts with a lot of variety Genius Party is good or Memories.
but as for full length series Beck (about indie rock in japan, not as good as the comic), Gantz(it has childish moments and bad voice acting but is quite mature) and Planetes (this has little to no action and is about basically space junkers, it from studio sunrise which mad e bebop).
also afro samurai, animation style is unique zany and hevaily tarentino inspired with a killer hiphop soundtrack by the RZA. It also features ron pearlman and samuel l jackson and culminates in a very mature tale of vengeance in league with Kurosawa's work.
but animated features by far have most of the maturity, things like Akira, Vampire hunter D bloodlust, Ninja scroll and milenium actress are roughly the same vintage as Bebop.
also Grave of the fire flies, but you have to watch it in japenese(its studio ghibli but not miyazaki, Post Nagasaki/hiroshima japan;it dosn't pop up on anime threads often enough).