I LOVE THE WHO!!!!!
also Santana - soul sacrifice - love the drummer -Michael Shrieve!
Sly and the Family Stone, Joe Cocker, and the Who were spectacular. These were the performances where you could not sit down.
Too hard to narrow it down but maybe for me (at the time) it was Crosby, Stills, Nash and Young who gave one of the best performances. I can still listen to any of the music from these artists and enjoy them.
Least favorite - Ravi Shankar. Okay. I'm just being honest. First day, near the very start. Boring. Boring. Boring. 
Now I'm going to check out the NBC website, Reb, and see what's cooking tonight.
Susan
“Half a truth is often a great lie.”
Ben Franklin
The Who
Jimi Hendrix
Sha Na Na
"The only thing that Columbus discovered was that he was lost"
The Band. None of their performance has ever been released. Still... they were one of the only bands who actually LIVED in Woodstock at the time!!! Oh, Michael Shrieve lives (& still plays) in Seattle now...
Joe Cocker as mentioned, my brother had boots almost like what Joe Cocker wore, his boots had a single silver star & red, silver, & blue metallic looking boots, I remember a pic of my brother standing on some big rig, showing off his biceps with worn out jeans & those boots! cool! 
dunno where the photo is, think his x wife has that photo.
also ten years after
The Red Hot Chili Peppers
"Harry, I'm going to let you in on a little secret. Every day, once a day, give yourself a present. Don't plan it, don't wait for it, just let it happen. Could be a new shirt at the men's store, a catnap in your office chair, or two cups of good, hot, black coffee. Like this." -Dale Cooper
Paul Butterfield Blues Band - Love March
Even little sister can do it!
Jefferson Airplane. I probably would have slept through their Woodstock performance though since it was early in the morning and been mad at myself had I been there.
-B
Bought Sly's burnin' Woodstock set (issued with the classic: Stand!). Performers who ALMOST made the fest: John Martyn (who was living in the REAL Woodstock at the time) & the original Jeff Beck Group. Ironically, the singer who WROTE the fest's anthem, Joni Mitchell, was unable to attend...