Witness by Sarah McLachlan. Still not sure what it means, but it speaks to me.
I was listening to a now-defunct podcast at work…typically, they would close the show with a random dance song or show tune – nothing too distracting. One day, they ended with a largely a cappella version of “Let It Be” that made me stop in the middle of whatever I was working on; I listed to it several more times, then listened to it several more times on the way home. It was apparently the studio recording of the same song from Across the Universe.
Not quite like a thunderbolt, but I still vividly remember the first music video I ever watched - “The World I Know” by Collective Soul. We didn’t have decent cable at home until I was in junior high school, so I had never really seen MTV even though I had heard of it. Having grown up in a conservative area and attended a religious elementary school, I had thought that I wasn’t missing anything (music television was just a cesspit of violence and sex, dontcha know), and I was very surprised to see a video that had some substance.
In 1985, kaylasmom and I were shopping in the Tower Records store in Honolulu, when I spied the album “Vocalese” by The Manhattan Transfer. I knew about the style from Lambert, Hendricks and
Ross and Eddie Jefferson, and I knew the Manhattan Transfer had some experience with it (Four Brothers, Birdland), so we picked it up and brought it home. When we put it on the turntable, we were blown away by one song after another.
But the one that REALLY knocked our socks off was Sing Joy Spring, Jon Hendricks’s tribute to Clifford Brown’s Joy Spring. I, for one, didn’t even fully listen to Move enough to appreciate it until a week later.
I have a history with Gerry Rafferty’s “Baker Street” that doesn’t involve thunderbolts, though there was plenty of other weird weather when it was playing on the air and I had to trudge out to the radio towers in the wee hours to take readings.
At a previous (and not as shitty) radio job, a fellow DJ and I schemed to sneak the song into the rotation past the likely objections of our stick-up-the-ass station manager/owner. To accomplish this, I performed surgery to excise the screaming guitar instrumental break, an act for which I still feel mild shame. 
Poker Face by Lady Gaga. I wasn’t even sure if I liked it, but I was instantly intrigued. What is this Lady Gaga??
Yes, definitely.
When I first heard Bach’s Jesus bleibet meine Freude as a teen, I thought it was the most perfect piece of music I’d ever heard:
But it wasn’t until this year that I got into Bach’s massive St Matthew Passion (double choir, double orchestra, six solo vocalists, nearly 3 hours long).
Many people have called it the greatest work of classical music ever written. I would say it is.
Last night I listened to the full Morrison Hotel album for the first time. Morrison was a dark articulate narcissistic artist. Capable of writing beautiful romantic yet disturbing lyrics. The Spy and Queen of the Highway articulated these two emotions. A lyric from Queen of the Highway is so honest:
MILD shame?! 
I remember being struck by this song also. For me, it was the searing, yearning saxophone more than the guitar, although that solo too was killer.
For hitting like a thunderbolt, it’s hard to beat “Thunderstruck”.
Late to the discussion but I’m going to say:
“Walking on Broken Glass” by Annie Lennox and
“Take Me To Church” by Hozier.
On the day I bought my first real stereo, I also bought the Rolling Stones’ Tattoo You. The first track is Start Me Up. It still takes me back.
Phil Collins- I Don’t Care Anymore. Just drums, bass pedals and guitar. Unique sound.
INXS- Never Tear Us Apart. Amazing start to the song and the greatness flows from there.
This recording of Well, You Needn’t by Thelonious Monk:
I thought I didn’t like modern jazz until I heard it. It changed my mind instantly.
Phil Ochs’ Crucifixion, performed by Jim and Jean.
Nine Inch Nails “Head like a Hole”. It seemed to express anger and outrage in a shiny new way. 
Those are good ones, this one hit me:
Then because i am a Angeleno:Randy Newman - I Love L.A. (Official Video) - YouTube
Then finally:
For years I thought the title was teenage wasteland.
Several songs in middle school:
Iron Man by Black Sabbath
Crazy Train by Black Sabbath
Master of Puppets by Metallica
Wasted Years by Iron Maiden
from that point on I listened to a lot of metal.
I’ll second Thunderstruck by AC/DC, but at that point I kind of feel like I had been already listening to a lot of AC/DC. Still a great song.
I found Been Caught Steeling by Jane’s Addiction, Angry Chair by Alice in Chains, and But Anyway by Blues Traveler intriguing the summer between high school and college.