Axis: Bold As Love - The Jimi Hendrix Experience
I think this is the band's best album. From start to finish, it's just an incredibly well-rounded record, featuring several of their best and most beautiful songs. Spanish Castle Magic, Castles Made of Sand, Bold As Love, and Little Wing are all here, along with some cool tracks tying it all together. It's just a wonderful listening experience.
I've never considered Hendrix to be a great lead guitarist, but easily one of the greatest rhythm players of all time. The way he so effortlessly fills the musical space with rhythm lines and licks is truly amazing, and a real treat to listen to.
http://www.youtube.com/v/uR5MpWgVxHk?version=3&hl=en_US
During the course of this list I was planning to nominate all three of Hendrix's first three albums (the official ones he wanted released), because they are all exceptional and groundbreaking for one reason or another. You beat me to this one.

Given D.B.'s comments, for those not aware: playing live, Hendrix would often play rhythm and lead at the same time. And, because his fingers were so long, he could stretch his hand all the way around the fretboard and use his thumb as another 'note-choosing' finger. He was also completely self-taught.
In addition, some of the things musicians now take for granted (e.g. phase shifters) were created by Hendrix so that he could get the sounds in his head out where others could hear them. He designed a speaker system where two speakers would rotate in their cabinets, giving the alternately 'open' and 'muffled' sound (later
this was done electronically). His 'instruments' were as much electricity itself in its role in sound production, and the recording studio, as the guitar. He knew how the guitar interacted with what was around it, altering its sound with whatever was handy, inducing feedback to punctuate and deepen the sounds and emotional effect he wanted to achieve [e.g. the sounds of bombs dropping in 'Machine Gun' on 'Band of Gypsys']. He played electricity and the studio every bit as proficiently as the instrument everyone knows him for.
[Yes, all but the link to phase shifters on Wikipedia was off the top of my head.]
This round is interesting because I'd already heard all but one of them, and there were samples of that one in its nomination.