Agualung from Jethro tull 
I was listining to the radio and heard this song, messed around on my acustic for a while and got got the riff down pretty goodthis riff is not to difficult             
"easy version"
e-----------------------I------------------------------I
B-----------------------I------------------------------I
G-----------------------I------------------------------I
D-----------------------I------------------------------I
A-----6--6--------5--4--I-----6--6--------5--4--2--4---I
E-----------5--6--------I-----------5--6---------------I

or if you want it to sound sound much better try it this way
"power chord version"
e-----------------------I------------------------------I
B-----------------------I------------------------------I
G-----------------------I------------------------------I
D-----8--8--------7--6--I-----8--8--------7--6--4--6---I
A-----6--6--7--8--5--4--I-----6--6--7--8--5--4--2--4---I
E-----------5--6--------I-----------5--6---------------I

good luck and good nite