A few random Irssi scripts I've written:
auth_quakenet.pl – authenticate using QuakeNet's CHALLENGEAUTH
coffee.pl – avoid accidentally sending commands like "·····/foo" to channels
scrollwarn.pl – avoid replying to old messages while scrolled up
server-time.pl – parse the time tags sent by ZNC on replayed messages
...and some that I've just contributed to:
cap_sasl.pl – authenticate using SASL PLAIN, EXTERNAL, ECDSA-NIST256P-CHALLENGE