Seems like we did these a little while ago...  Let's see if I can remember what I posted then.
 
Hazy Shade of Winter - Bangles version of the Simon & Garfunkel song
Green Manalishi - Judas Priest version of the Peter Green song
Daydream Believer - Monkees version of the Neil Diamond song
Song to the Siren - Lost Witness (Fabel Mix) version of the Tim Buckley song
 
Annie Lennox has an entire CD of wonderful covers (and so does Dream Theater).
 
Looks like most of the others I would comment on have already been listed...

Moshkiae
 
All Along the Watchtower - Bob Dylan I doubt that most of you have ever heard the original. But no one has ever NOT heard Jimi's version which is vastly superior! But while the guitar sings, the words do not have the sarcastic tone that Bob had in the original! Check out Guitar Player and one of the reasons why people love the Jimi version so much.
 

Frank Marino (Mahogany Rush) does a fair job covering Hendrix.
 
Incidentally, I would think that All Along the Watchtower by Dylan is anything but obscure - it's on his Greatest Hits volume 2, and anyone with even just a vague interest in his work owns at least that stuff. On these forums, I'd be tempted to assume that pretty much everybody is familiar with it.

And there's always the U2 version on Rattle & Hum. :P
 
I actually dug them a lot back then. Looking back, their music was a big part of my transition from playing and listening to music that consisted mostly of power chords to learning basic chords. I also discovered BB King through them.

craigb

Rain
I also discovered BB King through them.

And butterfly vibrato? 

Yup. :)
 
Do these forums have an influence on us? I've just ordered a few things off Amazon, including pH testing strips... My order was a few $ short of being eligible to free delivery, so I added the Rattle and Hum DVD. :/