Way too far back to remember the first songs (something out of the Mel Bay book).
But the ones that left an impression when I got them down...an acoustic arrangement of "Beth" that I still play...the intros to "Black Diamond" and "Rock Bottom"..."Goodbye To Romance"..."Mr. Crowley", "I Don't Know" and "Over The Mountain"...none of them note for note, but that's not what I was really shooting for.
Possibly the most euphoric moment? Finally figuring out the C#m on the bridge in "Can't Explain". In retrospect it was so obvious, but I kept missing it.