I like the rhythmic riff off "I am a pig" by Rob Halford
but the guitar riffs at the beginning of
The Hellion/Electric eye by Judas Priest are amongst my favourites.
Edit:- Actually I like anything by Judas Priest
Glenn Tipton and KK Downing are the riff masters!
I fully agree, Judas Priest's riffs are amazing and raw. Screaming For Vengeance is an excellent album, I also like Bloodstone, Riding On The Wind, Take These Chains, You've Got Another Thing Comin'...
Other Priest albums with great riffs are: Sin After Sin, Hell Bent for Leather, Stained Class, Unleashed In The East, British Steel, Point Of Entry, Defenders Of The Faith, Turbo, Priest...Live, Ram It Down, Painkiller, Angel Of Retribution, Nostradamus.
Rob Halford bands: Fight (War of Words, has dark-metal riff), Halford (Crucible, has killer riffs).
Cheers,