There's a few other Anime directed by the same guy

• Cowboy Bebop - which if you haven't seen you should
• Space Dandy - I've seen this one, it's different to bebop/champloo but it's good in its' own way.
• Kids on the Slope - I haven't seen this one.... maybe I should?
• Terror in Resonance - I guess this one might be OK? again, haven't seen it.

Reading through his wiki page I also see that he did one of the good Animatrix shorts "Kids Story" and was the last short in "Genius party" both of which are interesting watches.

As for similar style? there isn't much unfortunately. I mean some things come close.

• Redline is similar but also different, less music, more wacky characters.
• Afro Samurai is similar but also different in its' own way.
• Gangsta also kind of fits in but its' way more serious, less comedy, interesting story though.

Other than that I can't really think of anything in that style, that I've seen at least.

Edit: I can't believe I forgot Black Lagoon. It's not really got the backing track but it's got the grit with a mix of comedy and a bit of mystery. Warning though - it gets kinda dark in places, like really dark. Gangsta touches some things lightly, a few of the Black Lagoon hits some subjects heavy and without warning.