huh huh! that’ll teach me to try and correct typos on the fly!
Black Magic Woman - Santana
Aqualung - Jethro Tull
Everything above is good. I’ll add something that I think is different:
Joe Satriani’s “Flying In A Blue Dream.” 
At the beginning of “I’ve gotta know right now” (part of “Paradise by the Dashboard Light”) there is a great power chord progression.
Keek, please start a new thread on this worthy subject and I’ll be happy to reply with lots of suggestions.
I think Vai played The Devil AND Macchio’s guitar parts. I’ve read that in some guitar magazines, anyway.
I’d second any number of Allmans guitar parts - there are some fantastic riffs in Hot’Lanta, which is one of their less-known compositions - and the theme to Mountain Jam stirs the heart of any ABB fan in a special way. The closing riff to Dreams is very dramatic. Also, the riff to the electric Layla, which was actually Duane Allman’s contribution, not Clapton’s. (Although it’s borrowed from Albert King anyway.)
Sorry I got here late to the Zappa circle jerk, but I’d like to nominate his “Why Don’tcha Do Me Right?”.
And Devo’s “Come Back Jonee.”
Seek and Destroy is my favorite thing to play, and number 2 is No More Tears (Zakk Wylde is my HERO).
Along with these, I’d Have to say Paranoid by Black Sabbath, Fade To Black by Metallica, Demise Of Sanity by Zakk Wylde’s band BLS, and last but noy least WALK! by Pantera 
AMEN!!!
Without Muddy Waters there are no Rolling Stones, no Beatles, no Black Sabbath, no Led Zeppelin, no AC/DC. This is even more amazing considering the song was originally recorded in 1955!
Now when I was a young boy, at the age of five
My mother said I was, gonna be the greatest man alive
But now I’m a man, way past 21
Want you to believe me baby,
I had lot’s of fun I’m a man
I spell mmm, aaa child, nnn
That represents man
No B, O child, Y
That mean mannish boy
I’m a man
I’d like to add the riff in Heaven On Their Minds from Jesus Christ Superstar to this already impressive list.
Jeez, Bill lives on.
Another vote for Smoke on the Water.
Jailbreak - Thin Lizzy.
Achilles Last Stand - Led Zeppelin
Train Kept A Rollin - Aerosmith
Men Without Shame - Phantom Rocker and Slick
“Day Tripper” and “And Your Bird Can Sing”
Pink Floyd’s “Money” in general, but especially that descending run that leads into the instrumental bridge. The sheet music I have for the tune doesn’t include that fill and the TAB sites I have checked so far don’t include it either. Anybody have a link to that?
“On A Rope” by Rocket From The Crypt works for me. As does “Hate to Say I Told You So” by The Hives. And, “What’s The Frequency, Kenneth?” by REM. I like my riffs loud, fast and dumb.
I will go with Well Dressed Guitar by Deep Purple. Heavenly!! Dont miss this one!!
Slayer’s Raining Blood
I’ll also say GNR’s Sweet Child o’ Mine (It’s just so fun to play)
Jimi’s Castles made of Sand
Clapton’s Tears in Heaven
NOFX’s Linoleum
Pennywise’s Tomorrow
Whole Lotta Love and Black Dog by ‘Riff King’ Page.
I like playing the opening riff from Tubular Bells on my acoustic. It sounds really nice.
This Charming Man by The Smiths has a great guitar riff running all the way through.
Any few dozen examples from guitar deity Hendrix would also be on the list.
I can’t believe that no one has mentioned Eric Johnson’s signature song Cliffs of Dover. That’s gotta be one of the coolest main riffs ever crafted.
I’ll also add:
Metallica - Call of Kutulu, Master of Puppets (intro)
Blue Oyster Cult - (Don’t Fear) the Reaper, Burnin’ for You
and Weezer - Say it ain’t So