I'm going to post my openings in spanish, since my favourites are from my childhood 
(you will notice they repeat the chorus a few times...)
Exploradores del Espacio (Queen Millennia) - https://www.youtube.com/watch?v=xPC-tCre2Z0 (full song)
Has nostalgia all over it, damn Telecinco has the rights and will never release the spanish dub.
Oliver y Benji (Captain Tsubasa) - https://www.youtube.com/watch?v=wXMJgZzMJZU (full song)
Super hit everywhere it went!
Los Caballeros del Zodíaco (Saint Seiya) - https://www.youtube.com/watch?v=RTYIwv74fJQ (HD version)
Another super hit!
Now the childhood is done, and since Heidi has already been mentioned, here come random "classics"
Marco - https://www.youtube.com/watch?v=OPsQQFakmmA
Shin Chan - https://www.youtube.com/watch?v=a0XV5Gcdqxs
Neon Genesis Evangelion - https://www.youtube.com/watch?v=zbksWvNv-fU
FLCL since it's The Pillows - https://www.youtube.com/watch?v=Uh3lmE52GVc
