Two come to mind. Wizard in general. It wasn’t the first song I heard by the band, but when my Dream Theater loving self heard a few songs I kinda liked and then heard they could also do Wizard, I was like, “yep, fully onboard now.”
Then, 12/29/11 Bright Lights for opening my eyes to a new kind of improv I simply hadn’t been exposed to much before in my life. What a monumental jam that is.