I do have a personal favorite as well:
The Sting arrangement of Shadows In The Rain from The Dream of the Blue Turtles. Drivin’!
It’s also a beautiful illustration of how much difference an arrangement makes. The Police did Shadows in the Rain once–it was boring.
Yes.
More memorable ones - Sunday, Bloody Sunday - U2, and
Break on Through - The Doors.
<b>Voodoo Chile</b> by Hendrix
Where the Streets Have No Name by U2 - great build-up to the vocals, it gets more exciting as more elements come into the song - the keyboard chords with the guitar fading in, the bass and drums starting on the same dramatic downbeat, and as it all reaches its peak, the vocals take over. Yeah.
Who Do You Love by Bo Diddley (later by George Thorogood and the Destroyers) - the great bouncy Bo Diddley beat careens into and through the song raising ho-hum lyrics to “classic” status…
Perhaps the greatest opening “riff” - if you can call mariachi horns a riff - Ring of Fire by Johnny Cash - genius, pure genius throwing mariachi horns into a rockabilly/country love song.
Heartbreaker by Led Zeppelin
Money for Nothing by Dire Straits
First thing I thought of was “Paranoid” by Sabbath…no takers yet…wow!
“Heartbreaker” by Zep also springs to mind, although the “Opening riff”, as it were, seems to have been flubbed by an extraneous note…anyone else here notice that?
Paranoid by Black Sabbath (and the Dickies)
Stretcher Case Baby by the Damned
Godzilla by Blue Oyster Cult
Got The Time by Joe Jackson (and Anthrax)
I shoulda put Paranoid
I feel ashamed ! :o
One of the greatest opening riffs of all.
“Aqualung” by Jethro Tull.
Have you heard the Otis Redding cover? The opening riff is arranged for Tower of Power style horns, and it’s one of the funniest things I’ve ever heard.
And yet, this is so simple it is the only thing I ever learned to play on the guitar.
I would also like to note that a good many of these songs go downhill very fast after the opeing bit.
The offset on the quote led my eye astray. I thought, for just a second, that you were saying that Otis Redding had covered Aqualung. Eeeeeeek!!!
I have to agree, the horns (which I would describe as “James Brown Style”) are pretty darn funny.
I agree with pcarney. Those first few seconds of Voodoo Chile (the original one, not the Slight Return) are very cool. Other cool riffs by Hendrix: “Wait Til Tomorrow” and “Ain’t No Telling.”
Oh yeah, and regarding “Roll Over Beethoven,” That is a cool riff. So cool that Chuck Berry also used it to start
“Jonny B Good” “Back in the USA” “Carol” “Let It Rock” and “Reelin and Rockin” and probably some others that I dont know of. Almost all of his songs start in one of about 3 ways (with slight variations.)
Back in Black - AC/DC
'Nuff said.
IIRC: The opening few seconds of Good Golly Miss Molly (Little Richard) and Rock & Roll (Led Zep) are almost identical.
Nice to see some Tull fans here. 
Aqualung definately seconded (thirded - whatever). The start of Fat Man is pretty cool.
Louie Louie - The Kingsmen
Wild Thing - The Troggs
Gloria - Them
Journey To The Center Of The Mind - The Amboy Dukes
“96 Tears”- ? & the Mysterions
“Jumpin’ Jack Flash” - The Rolling Stones
“Evil Woman” - The Electric Light Orchestra
Kid Rock - “MY … NAME … IS … KIIIIIIIIIID!!!”
Also, the Specials - Ghost Town
Day Tripper - The Beatles
Hands down.
Sex pistols - Pretty vacant!
And not just the guitar - listen to the drum beat after the initial riff. Powerful stuff - shame the song goes downhill after that