Also, the opening riff of “Wild Thing” by The Trogs.
The killer synth riff from Elvis Costello’s “Radio Radio”.
The 'Floyd’s “Money” and that theme song from Perry Mason.
I SISOSIG–I came of age in the 80s. However, my parents were rockers, so I have to include In-A-Gadda-Da-Vida, baby. of ye ol’ Iron Butterfly, and, of course, Johnny B. Goode by Chuck Berry.
Also love Gimme Three Steps and Things Goin’ On by Lynyrd Synyrd, oh yeah, Ballad of Curtis Lowe (somehow that title doesn’t sound right, but ya know what I mean)
Great thread
Yeah, THAT one!
Opening to Dragnet Theme: dumm da dum dum…dumm da dum dum DUMM!
Jaws : duh dum…duh dum…dumdumdumdumDUMDUMDUMDUM…AAAGHHH!
Star Wars Theme: duh duh DUHH DAHH duhduhduh DAHH DAHH duhduhduh DAHH DAHH DUHDUHDUH DAHHHH!
Superman Theme: Bah dahdah dah dahhh bah dah dahh bah dahdah dah dahhh DAH DAHDAHHHH!
(tip o’ the hat to that ripoff artist John Williams)
That slap-base synth riff from “Seinfeld”
Rockford Files(!!): (buhduh da DUM) bweeedee dededeee dede dede dee deee deee (buhduh da DUM) bweeedee de de deee de de deee…oh, you know how it goes. Probably the most memorable analog synth riff of all time.
Gawd, the earworms!!!
I know it’s here already, but as soon as I read this thread title “Purple Haze’s” riff popped into my head.
While I agree that SISOSIG is a great riff, I purposely didn’t mention it because of the aforementioned ads. While I have nothing per se against popular music being used in ads, hearing it day after day kinda takes away a good riff’s charm.
Here’s an obscure one that came to me…“Tales of Brave Ulysses” by Cream.
Waaaow Waaow Wah uh Waaow…
Also “My Sharona” by the Knack
“Mainline Florida” by Eric Clapton
Dah, dah, DAAAAAHHHH. Dah, dah, DAAAAH DAAAAAAAHHHH. Dah, dah, DAAAAHHHH. DAAAAAHHHHH da da. Probably the easiest riff to write down as humming. And no, I’m not going to tell you what it is nor even if it’s been mentioned yet, but it’s the first thing that popped into my head.
Stupidly Happy by XTC.
On writing it, Andy Partridge repeatedly played it to friends asking which Stones song he had nicked it from only to repeatedly be told that he hadn’t.
I love XTC and paid homage to it in my song ‘I’ll Be Your Dog’. Seek and ye shall find.
MiM
“Here comes the bride”!
Rocky…and Indiana Jones themes.
I’m not a big Led Zeppelin fan, but how about Heartbreaker?
Pah. The Pac-Man startup tune preceded Mario easily. 
Though the mushroom power-up sound from SMB, now there’s a worthy video-game riff.
I second Black Sabbath’s Iron Man.
One of my personnal favorites is Judas Priest’s Breaking the Law. One of the most recognizable riffs I’ve ever heard.
That riff in Sympathy for the Devil is pretty cool and pretty memorable.
The Imperial March, from Star Wars.
The opening of the X-Files theme.
The organ riff from “Light My Fire”.
The guitar lead-in to “I Want To Hold Your Hand”.
There seems to be some confusion here about what a riff is. Anyway my candidates:
Whole Lotta Love. Am I really the first person to name this?
The Peter Gunn theme. Even if you’ve never seem the show (and who has) you do know this one.
The into of Tubular Bells
TV themes:
Mission Impossible. (not the f**ked up film version).
Stingray.
Any CSI.
Doctor Who
Roobarb
Loopydude I love the Rockford Files but that’s more of a tune than a riff innit?
I refuse to mention Bob the Builder, oh, oops.
How about Sportscenter’s “DA-da-DA! DA-da-DA!”
anybody with me on this one?