"Knockin' on Heaven's Door" by Bob Dylan. Its only four chords.

Heart Shaped Box

Agreed, although when I first started guitar it took me a while to get the distortion right on the solo.

I play guitar as well it is difficult, it took me a week to figure that out now I play it perfectly.

It took you a week to learn to play guitar perfectly? ...i really am tryig to make sense of that sentence...

No just Heart Shaped Box took me a week to play perfectly I played that song non stopped. It took me a year to play half way decent I'm still not very good.

Black sabbath - its only 3 notes

Tenacious D - One Note song ;)
Step 1. Learn fretting a note and string bending
Step 2. Play the song.

Smoke on the water definently because it can be played at ant difficulty like with single pecks with a pick or with power chords or even normal chords lol