A filksong is, as mentioned in the header, a song parody. You listen to the song and try to write lyrics to match--quite hard, as you have to make sure that accents and stuff are emphasized in addition to making the lyrics as funny as possible.

/pomi/filksongs/type starwars.txt

These were originally found on the Star Wars Humor Home Page, but I figured what the 'ey, may as well put them on here, too...

If You Wannabe a Jedi - to the tune of "Wannabe" by the Spice Girls - The first filk I was ever fully satisfied with.

A Tribute to the Lord DV - to the tune of "MiB" by Will Smith - The first filk that anyone else was ever fully satisfied with, thus explaining how I got more than two pieces of mail on it.

/pomi/filksongs/type anime.txt

[R1/2] A Pretty Fine Iinazuke - to the tune of "Pretty Fly (For a White Guy)" by the Offspring - I posted it, realized I wasn't fully satisfied with it, then changed the "numbers" line so that it rhymed...and lo, it was good.

[R1/2] The Students of Furinkan - to the tune of "Knights of the Round Table" by Monty Python - Written during the entire Ranma Python craze on the FFML. That's MY excuse, anyway. :P