My favorites have to be
Trigun and
The Twelve Kingdoms. The latter starts off as a very typical (nearly stereotypical) anime, and I stopped watching after the second episode. The main character was just too annoying. During my second viewing, I decided that the main character wasn't merely annoying; she was behaving as anyone could expect a teenage girl to behave given her situation.
The Slayers was my favorite in high school, but it's fallen to an "okay" status since.
Blue Seed was fun the first time through, but I didn't enjoy it as much the second time. Perhaps the first and second viewings were too close together, but I'd have no problem watching Tri-Gun or Twelve Kingdoms multiple times in a year. I don't mean to sound like a snob, though! My taste just changed, and I'd probably enjoy watching those two with a group just as much as I enjoyed watching them alone the first time around.
I don't recall seeing any anime on Nickelodeon, though I know how much some people want to classify
Avatar as anime, even though it isn't. I haven't watched any Nickelodeon beyond that since they ceased showing cartoons in the same spirit of the original Nicktoons. I'll revisit the channel (through Hulu) when
The Legend of Korra premies next November.
It’s okay. I’m with the band.