Wow, I'm surprised I haven't posted in this thread. Anyway.
Cardcaptor Sakura - This anime makes me so nostalgic. I love everything about it, the animation, music, characters. It has such a high rewatch quality and it never has gotten old.
Tsubasa Reservoir Chronicle - Tsubasa is deceiving. You think it has this nice circumstance where the main character is in trouble and her friend rushes to save her. There is so much more to it, and the way the characters develop and change during the series is great.
Kino No Tabi - For 13 episodes, it was just a nice series. Kino goes to all these different places, and so many lessons about life are taught from the people she meets.
Gurren Lagann - One of the only mecha anime you would see me watching, it just has so many awesome battle scenes, and is an anime that really takes chances.
Kaze no Stigma - I just like this one. I've heard the manga is much darker toned, but the anime still has a lot of laughs.
Haruka Nogizaka's Secret - Finished the first season the other day, and just seeing Yuuto and Haruka's relationship, her secret anime/manga obsessions, and all the funny misunderstandings makes it hard not to love it.
Sweet Valerian - It's almost like, the Powerpuff Girls, in CLAMP's style. Enough said.
Fullmetal Alchemist - It was one of the first series I seriously got into. If any anime taught you something, it would be this one. I include Brotherhood when I say this too.
CLAMP School Detectives - The amount of trouble these kids get into, I just can't not love this series. It has a lot of cute moments.
Elemental Gelade - Even though I hated the animation, hated the voice acting, the fact that it is off one of my favorite manga makes me love it. And, because it is one of the few series that has a clear ending.