Buffy the Vampire Slayer will keep you occupied for a LONG TIME. Seven delicious seasons. Chances are if you like Sailor Moon this might be up your alley. Tru Calling is pretty good too but it never finished.
Firefly is absolutely fantastic, tragically only 14 episodes.
Always good to watch Neon Genesis of Evangelion, Cowboy Bebop, Outlaw Star, Trigun, Rozen Maiden, good stuff. Also, if you like Sailor Moon you might enjoy the show Pretear. It's like... a Snow White/Sailor Moon story... weirdness... thing.... It's not bad . I think artists for Sailor Moon worked on Pretear because it uses some of the exact same storyboards that Sailor Moon does.
Dexter's absolutely incredible if you're into watching a show about a serial killer who kills serial killers oh god it's so good I need to catch up on like two seasons of it though.