I can’t think of the last one to grab me instantly. I’m sure there have been a number of them, but the absolute best song I’ve heard and loved instantly was “Dry the Rain” by the Beta Band. Yes, it was due to the 5-10 second clip in the movie “High Fidelity,” and I’d have bought the record right away if I’d been a character. Instead, I bought the record the next day in real life. That’s a song I can listen to over and over and over, and the only reason I’ll move on is a mild fear that I may come to regret a 50th straight listen.
I love this song, too. It makes me cry every time I hear it, though, because our house burned down last year. 
It kind of pulls out that healthy, emotional stuff out of me.
Reminds me of Robert Plant/Led Zeppelin
Iona - Wave After Wave
The Mountain Goats - Store
Dan Walsh - Every Day Is A Better Day
i just got the Flying Colors cd - my favorite is The Storm, but there are a lot of good songs on that album. Wonder if they’re gonna tour?
I also like “Banker Bets, Banker Wins” from Ian Anderson’s Thick as a Brick 2.
“Royals” by Lorde:
Also, “Don’t leave me” by Regina Spektor:
And “Love Letters” by Ketty Lester–it’s been an earworm for me lately:
Damn good song!
“Moves Like Jagger” by Maroon5
I found this cover of “Come, Little Children” instantly arresting. I played the video I originally found it on several times to listen to it, then went looking for other music by the singer. After listening to a few pieces, I bought everything she’s recorded. I suppose that means one of the other songs I listened to before buying is technically the last I heard and liked instantly, but the linked song is the one that got me moving.
Ke$ha division: “Machine Gun Love”
Non-Kesha division: “Can’t Hold Us,” Macklemore and Ryan Lewis
Green Blood by Sonny and the Sunsets. Had never heard of the band before. Loved the song instantly.
The Basket or the Blade by Enter the Haggis.
Six Pack by Jeff the Brotherhood. Heard them on Letterman, then kept hearing the song in stores, etc. after that. Has a good 1970 feel to it.
- Scream (Acoustic) from Chris Cornell (commercial Timbaland version blows)
- Destroyer of the Universe - Amon Amarth
- Another Day Another Way - Volbeat