Define best? One that sticks in your head? One that's technically brilliant? One that invokes emotion or memories? One that every one knows?
I don't know where to begin, or where to stop.
Seriously - when you got as far as "Peter Green's Fleetwood" did you not already start hearing the intro to Oh Well before even getting to the first comma?
Absolutely. That and Shake your Moneymaker.
Jimi Hendrix, Purple Haze.
The Animals - House of the Rising Sun (although their version is poop when compared to Bob Dylan or Pete Seegers).
Chuck Berry, Johnny B. Goode (although Jimmy Hendrix' version is much better).
The Beatles, I Feel Fine (probably not the greatest, but whenever I hear that song, the intro is stuck in my head for days).
Another Beatles riff that gets stuck in my head for days is the intro to Ticket to Ride (but probably because Ticket to Ride is one of my favourite songs of all time).
Ocean Colour Scene Riverboat Song
This one is iconic (not sure about over the pond, but over here it is). Folks will probably have heard covers, not the original.
Great, great band that (aside from this song) never got the attention they deserved. The bassist went on to form another band called Cast who were no where near as good. The Lead singer of the Las was asked if he wanted to get back into music again, but he said he didn't see any point as every 3 months he gets a royalties cheque from this song which makes him a fortune.
Intro to Step in to My World by Hurricane #1?
Fools Gold by The Stone Roses?
or Waterfall by the Stone Roses?
Tonnes from my youth/when I was a teenager and there are even more from the eras where music was consistently decent.