When I first really got into music it took me a while to decide if I liked songs or not and they gradually grew on me. Nowadays I know within one listening if I'm going to like it.Whilst not necesarily my faves below are some that really hit me from the word go:

Satriani - the extremist (saw on TV, noisy mothers. Couldn't believe it was real!)
Senser - Age of Panic. Angst ridden rock/rap, much prefer these guys to rage who are much more famous. Brilliant lyrics/original music.
Rush - 2112. did't hear this for years after I became a fan of their music. Love it!
rush - Xanadu. Try the version on exit stage left. Cool!
Pink Floyd - Comfortably numb.
Prelude 1 - Sentience, from a guitarist magazine. Beautiful, superb piece of music from a virtually unknown duo from oz. Soulful violined guitar, creepy interludes, great tunes.... I was going insane before I heard this song and it expressed everything I felt, all the saddness, pain and wonder.
Allanis Morrisette - Thankyou. Simple song but very poignant had to listen to it repeatedly when I first heard it.
Gottschalk - Manchellier (classical piano), my dad used to play this on CD when I was a kid. I still love it.