I've been really digging the Season 2 OP for My Hero Academia myself. It's got kind of a mix of Japanese rock and power pop to me, which I guess is why I like it:
even though its the second worst part in the series, i feel so nostalgic after listening to this (especially after having finished watching every episode)
second favorite of all the HxH EDs
...but ED5 was so good they decided to use an alternate version of it for ED6
My favourite ending is Kimagure Orange Road ED 2, "Kanashii Haato wa Moete Iru" ("My Sad Heart is Burning"), performed by Kanako Wada, both for the song and the unconventional chalkboard animation (or at least I think it was done on a chalkboard).
Here's a live TV performance by Kanako Wada of the song from 1987.
One opening I really like is Kamichu!, which had the other "Hare Hare" theme song from 2006, "Hare Nochi Hare" ("Sunny Days Followed by Sunny Days") performed by Maho Tomita. I especially like the gimmick of incorporating the credits into the art.