What about the In and Out Of Love riff? I think that sounds excellent live and I'd love to be able to play it. A lot of the good riffs sound simple to play such as Eric Clapton with Layla, Deep Purple with Smoke On The Water, Led Zeppelin with Whole Lotta Lovce, Houses of Holy, Kashmir, etc, but I bet they are far from simple. A guitar riff can make or break a song really. The good ones are remmebered and the bad ones are forgotten. I'd certianly love to be able to play some of the simple, but good ones, Maybe I should take up playing guitar.

Another good riff, is from Wanted Dead Or Alive. That sounds awesome on an acoustic.