Well, it's official. Cowboy Bebop is the greatest anime series of all time. Well, ok, that may be a bit of a hyperbole, but not much of one. It has a legendary status that the latest shonen idiot-fest, the most popular shojo pretty-boy romp, or even series' like Death Note or Code Geass can never hope to achieve. If you like anime, you've at least watched Cowboy Bebop. If you haven't, what the hell are you waiting for? Even if you don't end up liking it (despite my gushing about it, it can be a real love it or hate it thing), you should at least give it a watch once in your life.
This show has also had a massive impact on the anime industry. Various members of the production team for this show banded together to form a little studio named Bones. They're the masterminds behind not only the Cowboy Bebop movie, but also Wolf's Rain, RahXephon, Eureka Seven, Ouran High School Host Club, and of course Fullmetal Alchemist (as well as the direct manga adaptation, FMA Brotherhood). Yes, both of the FMA anime were made possible because of Bebop.
I'd go into depths of why it's so good, but it's been beaten to death and beyond. Suffice it to say that the story is wonderful, the characters are some of the best and most memorable ever, the animation is flawless, the English dub is ridiculously awesome, and the music is done by Yoko Kanno (no explanation needed). If I can think of one flaw, it's that the episodes Wild Horses and Boogie Woogie Feng Shui are pretty weak in comparison to the rest of the series, which is bizarre considering that interspersed between those two are Pierrot le Fou and Cowboy Funk, two of the strongest episodes in the series (ESPECIALLY Cowboy Funk). Other than that though, you should definitely check this one out.