Some of my fav. opening Riffs (you know these songs just after the 1st of 2nd note.
AC/DC - You shook me all night long
Rush - Limlight
Asia - heat of the moment
Def Leppard - Photograph
Dire Straits - Money for Nothing
Guns N Roses - Sweet child of mine
Heart - Beracuda
Ted Nugent - Cat Scratch fever
Truimph - What's another day of Rock n Roll
And oh, so many more.
A similar thread and maybe more challenging would be the most reconizable / fav. bass lines.
For example: Queen - Another one bites the dust.
http://www.youtube.com/watch?v=rNQRfBAzSzopaul