this is a groovy simple riff that i've been playing forever, don't 
remember where it came from...
anyways, its the standard blues 12 bar type thing, you don't have to 
play it in the set number of repititions i made (4x, 2x, etc), but its
"musically correct" or whatever. i just made up the ending, so it 
gives a bit of finality to the riff, but its really easy to just throw
in some of your own solo's to give it some flair. 

knock yourself out!

play 4x  [G7]
e|-2s3---------------------
b|-2s3---------------------
G|-----5-3s4---------------
D|-----------5-------------
A|-------------------------
E|-------------------------

play 2x  [C7]
e|-7s8---------------------
b|-7s8---------------------
G|-----10-8s9--------------
D|------------10-----------
A|-------------------------
E|-------------------------

go back to first riff, play 2x, then the grand finale:

  [D7]               [C7]           [G7]
e|-9s10----------10-|--7s8--------8-|-2s3-------3---------|
b|-9s10-------------|--7s8----------|-2s3-----------------|
G|------12-10s11----|------10-8s9---|-----5-3s4-----------|
D|------------------|---------------|---------------------|
A|------------------|---------------|-------------3-5-0---|
E|------------------|---------------|-------------------3-|

[G7]     [C7]    [D7]
e|-3--  e|-8--  e|-10-
b|-3--  b|-8--  b|-10-
G|-4--  G|-9--  G|-11-
D|-3--  D|-8--  D|-10-
A|-5--  A|-10-  A|-12-
E|-3--  E|-8--  E|-10-