The opening for Watamote, I really like. The anime itself is pretty bad, though it was fun to drunkenly watch with a friend. - This

Tank! from Cowboy Bebop is one of my favorite classics, though really the entire Bebop OST could be on that list.

OP1 from Ranma 1/2 is a fun listen.

And every Creepy Nuts song in Call of the Night is an absolute banger.

ED1 - Yofukashi no Uta

OP1 - Daten

ED2 - Nemure

OP2 - Mirage

And several other insert songs. Easily some of my favorite anime music atm.