Okay, of course I'm going to start with...
Gurren Lagann OP ED1,
ED2
All three of these songs fit the series just perfectly. I can't actually find much else to say about them, just look at how damn great they are.
Slayers NEXT
Okay, I just really fuggin love this song. Great build-up, more build-up... and then BAM. WE'RE GOING ON AN ADVENTURE! The opening animation is also well put together, with some foreshadowing but nothing too obvious.
Mawaru Penguindrum OP1
This one definitely blew me away when I first say it. All the visuals and lyrics fit into the whole "train station" and "destiny" themes that the show has going on. The soft voice and the magnificent orchestra go together so well it's a crime. I wish they kept this as the opening for the whole series. Also, y'know how I mentioned how the Slayers intro has a bit of foreshadowing? Penguindrum masters it. There's foreshadowing EVERYWHERE in this opening.
(unfortunately the opening isn't on YouTube)
KIMI DAKE WOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
Soul Eater OP1
DAT RIFF. DAT BEAT. God DAMN is this opening good.
This was the first thing I ever saw of Soul Eater. Next thing I knew I was watching the whole series and loving it.
Cowboy Bebop
Just because I want to be the first one the mention it lol
This one's pretty much universally loved. Like cake. Show it to a non-anime watcher and they'll probably find some liking to it. Same with
Baccano!
Steins;Gate
Another case of I JUST REALLY LOVE THIS DAMN SONG. As much as I love this show so it fits. ;P
Neon Genesis Evangelion
To me this song rocks. It's a shame it doesn't match the rest of the anime. I've said this before this opening is in a nutshell "AW YEAH ACTION! GIANT MECHS! SHADY ORGANIZATIONS! YOUNG BOY WILL BECOME A LEGEND!" and the show then says "LETS ALL GET DEPRESSED!" So the exciting opening was one of my favourite parts of the show.
Nichijou
OP1 OP2
Hyadain <3
BLEACH! OP1
This is back when Bleach had to make something that stood out, when they had to make something stylish and eye-catching for an opening. Unlike now where it's "lol it's bleach and you're already watching it" This is what got me interested in Bleach. What got me to watch the show when I was a bit younger.
OP193759836589365WHATEVER
I really like the style they went with for how the characters looked. Maybe I just like SID. They have a thing for doing really awesome "OMG THIS IS ALL FINALLY COMING TO AN END" songs. Which is also the case in...
Fullmetal Alchemist Brotherhood - OP5
WHY CAN'T I HOLD ALL THESE EMOTIONS
Seriously, it didn't even rain in the ending, then why is this so amazing?
I also love
OP1 Again.
Dantalian no Shoka
Okay, maybe fighting a giant rock monster didn't go too well, but everything else fits awesomely.
Ben-To
IN STARK CONTRAST TO THE LAST ONE this opening is actually... done really well. The action matches the beat going on perfectly and the whole song reminds me of the 90s feel that Slayers NEXT's opening had.
Gantz
Don't watch this anime. The ending sucks.
That said, this song matches the series
feel SO DAMN WELL. More than most other songs on this list match their respective anime. After going through the manga I can imagine if they kept the anime going for 200+ episodes. But I CAN'T imagine anything else being the opening every time but this.
Persona 4
IT'S BREATHTAKIIINNNNNG MOMENTS IN RIIIIIIFE.
ADDICTED TO MY RICE CRAVING! MORE AND MORE!
I love you.
I'm going to do my favourite endings later.