Here are the parodies I have been able to find at Mudcat:

A MICROSOFT CHRISTMAS, anonymous.

TWAS THE NIGHT ETC., by Harvey Ehrlich.

THE NIGHT BEFORE CHRISTMAS AT M' HOME ON THE RANGE by "Cowboy King" of Arden Hills, MN

THE NIGHT BEFORE CHRISTMAS (IN TEXAS, THAT IS) performed by Gene Autry.


There are also these threads, which contain lyrics created in round-robin fashion by several Mudcatters:

BS: Twas the Night Before a Mudcat Christmas, 1999.

Mudcat night before xmas2000

Twas the night AFTER mudcat Xmas...., 2000.

BS: The Night Before Mudcat Christmas 03, 2002.

Song: Twas t' night before Mudcat Christmas 03

Folklore: Twas t' night before Mudcat Christmas 04