YACC: Yet Another Compiler Compiler.
YAST: Yet Another Setup Tool.
YAPC: Yet Another Perl Conference.
YaBB: Yet Another [Bulletin Board]?.
YABA: Yet Another Bloody Acronym (see TLA).
YAUN: Yet Another Unix Nerd.
YAAP: Yet Another Ascension Post (people who play Nethack will know what this means all too well...).
This jargon is also used in non-abbrieviated form, and the inevitable 'Yet Another YAPC report' has also been used.