I was surfing some filk music sites today (Saturday February 28, 2004):

"The maiden watches helplessly throughout the whole attack,
Then hacks up half the hoodlums with one hand behind her back.
The lady makes a gesture, and the other half are fried.
Their guardsmen gesture back, as they lie dying on the side."

...I laughed until it hurt!
Here are some more sites:
http://www.prometheus-music.com - found recently
http://www.prometheus-music.com/eli/fishltr.html - biography of Leslie Fish
http://www.hobbyspace.com/Music/music7.html - Space Filk: "Minus Ten and Counting" (recoommended) and others.
http://www.firebirdarts.com - heir apparent of "Off-Centaur Publicationss".
http://www.filk.com

See my little tune whistler on my computer page for the tunes to a few filk songs, etc.
Other music on my website

"Mr. Compatibility" -- found on this interesting website: http://www.physics.ohio-state.edu/~bcd/ (July 12, 2005)

Etymology of "filk"
The explanation that I read is that the term "filk" arose from a typo on a fan publication where they were trying to indicate "folk" singing, and it fit the type of weird stuff that F&SF fans were composing so well that it stuck.