I always get hooked on the main riff of the song "Breadfan" by Budgie, it's spiraling intensity is just so intoxicating.
I also am posilutely (yes, I just made up a new word) hooked on the acoustic beauty Pete Townshend creates on The Who's "Mary Anne With the Shaky Hand", if I had to pick one word to describe the sounds achieved in between the verses, I would have to use something like "wizardly". As well, the energetic, pop-inflected riffing on "Out in The Street", is probably one of the best things that Pete ever put down on record. And I won't even think of leaving out "Baba O'Riley", those power chords blow me away with their gut-wrenching power every time.
But now, since it would take me forever to list epic riffs, I'll just go by the individual guitar sounds in songs which I find most effective. The first of these is the guitar growl produced by Steve Lukather in the tail-ends of the chorus of the Toto song "Africa", the second sound which I absolutely love would be the opening bars of Stevie Ray Vaughan's "Love Struck Baby", it just too cool for me NOT to love it. I also quite enjoy listening to Robbie Robertson's guitar tone on The Band's "This Wheel's on Fire". And the final guitar sound which seems worth mentioning to me at the moment, is the opening G chord of Badfinger's "No Matter What", Seriously! That chord SPANKS! Probably one of the most forceful, heavy-hitting sounds produced by a band outside of the Heavy Metal and Hard Rock genres.
Just a few I can name off the top of my head. I tried to avoid solos, but On the Loose has a pretty sweet solo (though I don't know if it is, by definition, a "solo" if it's mixed with keyboards).
And I apologize for sticking a country song in there. :P