Van Halen's "Respect the Wind"
John Mayer's "Comfortable" {i love the acoustic in this, i have a friend who plays it for me all the time. such a turn on lol}
Led Zepplins "Stairway to Heaven" and "No Quarter"
if you going acoustic stuff jack johnson, matt costa, ben harper, donavon frankenreiter almost all of their songs are pretty cool sounding some more then others.
electric jimi hendrix has got amazing songs, ozzy osbourne crazy train/momma i'm coming home.
not sure if you consider this an answer because it doesn't really have a good riff, but I like the melody of it. The song "all the same" by sick puppies. The song itself is okay but I heard an acoustic cover on youtube the other day that killed.
i actually have all his albums, box set, etc. ive also read the biography about him, and it amazed me the stuff he was able to learn with a guitar (pride and joy is my wife's song, lol). i think its funny how he never thought himself a good singer, but his voice definately fit his style of guitar playing
AC/DC well most of their songs have good riffs i myself can play T.N.T, thunderstruck, it's a long way to the top and a few others
guns n roses - sweet child o mine, classic song with a riff i can play
oh these are electric.
green day - time of your life easy riff using shords on an acoustic guitar and the first song i learnt to play