It varies day by day.

Today it would be "London Dungeon" by the Misfits.

when I think of the term guitar riff
my mind immediately goes to the heavy part of "Bring it on Home" by Led Zeppelin

probably not my favorite
but it instantly pops into my head

It's on Faust IV - you know the one... it goes on forever like the theme tune to an 80s car show. That one.

The verse from Jimi Thing, by Dave Matthews.

I'd like to pick something cooler, but I'd be lying.

david bowie. rebel rebel

i love playing it too

The Scientist's Solid Gold Hell

"52 Girls" by the B-52s.

Probably "Brother James" by Sonic Youth. But maybe "After Forever" by Sabbath. "European Son" by the Velvet Underground comes immediately to mind too. "I Wanna Be Your Dog" is right up there too.

Led Zeppelin - Good Time Bad Time

captain beefheart - big eyed beans from venus

constantly evolving... i like!

I may get ran out for this one, but another two of my favorites would be "The Everlasting Gaze" and "Pissant" if only for the sound of it.

Which riff exactly? There's like 20 really thought-out and intricate riffs in that song. I wish someone would tab that...

Hey now, this ain't "all time favorite guitar TONE"!!! Hah.

I don't know if I have an "all-time" favorite riff. Right now, I'd say it's We Are Time by The Pop Group.

Wingwalker - SHELLAC
The Lee part on Skip Tracer

i get really hooked on Furniture by Fugazi

Cities on Flame w/ R'n'R
The Red and the Black

it's more the two constantly evolving riffs in your left and right speakers. but the two riffs combined at 0:25 are stellar.

part of the tab: click

Yourself in the World by Proudliot
or
Arnold Lane by Pink Floyd

Obvious, perhaps, but "Gloria" and "All Day And All Of The Night" are pretty hard to fuck with.