"Wonderland" - OP11 for Gintama. Really bright, energetic and I love the song. I would say "Sakura Mitsutsuki" (OP13) and "Tougenkyou Alien" (OP9)
were better thematically, and "Pride Kakumei" (OP15) comes really close to Wonderland, but Wonderland wins by a hair.
"Period" - OP4 for Fullmetal Alchemist: Brotherhood - Not as heavy on characterisation as most of the other FMA openings, but mixes in it well with a lot of good action shots, which don't really spoil anything. Honorable mentions to "Again", as well as "Rewrite" from the original.
"Peace Sign" - OP2 for My Hero Academia is super catchy. Also really starts developing on the themes "The Day" set up.
"No Pain, No Game" - Btooom! is a really exciting theme for a pretty average-yet-still-watchable anime. The song really makes it, though.
"Sono Chi No Sadame" - OP1 for JoJo because JoJo needs to be included. I also loved "Chase" for setting the scene for JoJo4.
And finally, "Mob Choir 99" - Mob Psycho 100, a great opening for a great show. Chock full of inside jokes and references, without spoiling. Kind of confusing without hearing the full song, since I'm pretty sure 81 doesn't come after 40.
Also, needless to say, "Database" by Man With a Mission.