I've been having entirely too much fun with this thing:
http://uploads.ungrounded.net/147000/147276_punkomatic.swf
This is probably my favorite of the ones I composed. Click 'load' and paste this string into the text box. Then play it.
--------6-7878787876-8883---3-5-6-7878787876-889--------------------------------------0---0---a---a---a---a--b--a-b-b6-0---a---0---a---a-b--------------------------------a-a-a-a-a---1---3-2-4-5-a-a-a---9--3-2-4-5-0---a-------------------------------------
try it yourselves and see what you come up with.
And if you care, here are some others I made:
----------780--80--80--80--84-4-4-4-4-4-4-580-480-480-489----------------------------1-3-3-4---6-1-3-3-4---6-1-3-3-c-------1-3-3-4---1-3-3-4-c---b--------------------------2---2-4-2-4-2-4-2-4-9-4-3-4-a---------9-4-3-4-2-4-3-4-a----------------------------
999799979--74-5-9-94-3---3---3---9---9--9-99984-4-4-4-4-9998989-89---9-------------------b---b--0---b---0---5-0---6-c---c--c-cccc6--0---5-3-2---a-3-3-c---b-------------------a---4-1----a---430---4359-9-a---a--a-aaa9-1---0-1-2-431---a----------------------
----3---3---888888889--3---3---3---888888889--9---------------------------------------9991-5-1-5-6-6b----9991-5-1-5-6-6-6-6b----999b------------------------------------------767-767-a9-4-4-a---767-767-a9-9-4-4-a--------------------------------------------