Russian Roulette is a sure in.
Then we have the ending of the last episode of Maria Holic Alive. Shit's cash, etc.
From *monogatari I better include only one... but which? Snowdrop? One of Nadeko's? Kimi ga Shiranai Monogatarai? Hitagi's Nise op? ...probably snowdrop after all.
As for SZS the problem is easier: even though practically all openings and endings are 3x3 material, I can just choose the three minutes version of Ringo Morige Beam and stop thinking about it there.
And Pani Poni Dash is ... impossible. Kiiro Vacances, Roulette Roulette and Shoujo Q are all perfect. There's no choosing between them, so I guess I will throw a die or something.
Now, for the stuff that may actually fall off the list:
Natsu no Arashi s2's opening. That was one of Shaft's finer works, may I say so.
Kyousogiga's TV opening. I loved the song ever since the additional ONAs, the way they made it into an opening was marvelous.
Hidamari has so much good openings and endings that I wonder if I can choose one... wait... I can. Honeycomb's ending was way too beautiful.
Soredemo's ED was genius tier
Also, Servant x Service had a truly wonderful OP. The same guy traditionally has good openings, but that one was the best.
Sketchbook's OP is one of the most relaxing things ever
Jinrui had great op/ed too... which one should I include?
Same for Dantalian; probably the opening, as the ending was 12/10 as a full song only.
Kyoran Kazoku Nikki, especially Kyoka's ed...
Tonari no Seki-kun's jazzy ED...
AAAAAAAAAAAAAAAA I AM GETTING NOWHERE WITH THIS