Baccano!,
Cowboy Bebop,
Samurai Champloo,
Steins;Gate, and perhaps
Outlaw Star.
Then it depends on what you prefer from a dubbing perspective.
Baccano! and
Cowboy Bebop have stellar English dubs, but for me,
Samurai Champloo and
Steins;Gate "clicked" a little better with the original Japanese dubs because it feels more authentic for anime shows actually based in Japan.
Outlaw Star is a bit iffy on both ends of the dubbing spectrum, but the writing and plot overall are generally good enough to overlook it.
Baccano! is... well, tough to describe. But it's set in Prohibition-Era US and I like to think it's what you'd get if old-school Quentin Tarantino or Guy Ritchie made an anime. It may not be for everyone, I suppose, but I thought it was absolutely fantastic.
Cowboy Bebop is a space-western (other notable examples of the genre include
Firefly), and the "main" character of the ensemble cast in English is voiced by Steve Blum. Bitches love Steve Blum. More seriously, it may be over a decade old but it still holds up to even better standards than some more modern anime shows.
Samurai Champloo was made by the same guys responsible for
Cowboy Bebop (the English dub even has quite a few recurring voice actors), but is set in -- I think -- Feudal Japan. With samurai and kimonos and one of the main characters in English is again voiced by Steve Blum. Really nice balance between absolute hilarity, high-octane action, and more somber, slow moments in both of them.
Steins;Gate is a modern-day sci-fi show that really delves deeper into heavy subjects, and includes time travel, a fair bit of techno-babble, and a tsundere redhead love interest.

It's got some slow pacing to start with, the first six episodes or so feel more like a slice-of-life comedy than anything else, but once it gets going it really gets going.
Also, the Japanese dub gives us such gems as this:
And I'd describe
Outlaw Star as what you'd get if you crossed
Cowboy Bebop with
Dragonball Z. By which I mean it's a sci-fi shonen series (think
DBZ,
Naruto, etc.) and certainly feels as such. Lots of fun action, funny dialogue, a bumbling comic-relief character, censored nudity if you get the original English releases... it's got it all.
They're all 26 episodes or less, as well, so it won't completely destroy your schedule to try following through on them.