These are just the scripts I have written or modified for Irssi, probably usercount, nickcolor and title are the most popular scripts here. You'll find many more scripts in the scripts archive.

akill.pl	Intelligent akill command (11 June 2006)
chanact2.pl	Adds new powerful and customizable [Act: ...] item (chanelnames,modes,alias). Lets you give alias characters to windows so that you can select those with meta- (07 July 2006)
clones.pl	/CLONES - Display clones in the active channel (with added options) (23 January 2002)
conncount.pl	Counts connections and shows them as a statusbar item (for opers) (11 May 2004)
dccself.pl	/dccself ip port, starts a dcc chat with yourself on that host/port, best used with /set dcc_autochat_masks. (24 March 2002)
file.pl	A command to output content of files in various ways (17 September 2003)
foreach_user.pl	Extends the /foreach command to have /foreach user (users in a channel). Syntax: /foreach user [hostmask] command. (31 December 2002)
nickcolor.pl	assign a different color for each nick (06 July 2003)
on.pl	/on command - this is very simple and not really designed to be the same as ircII - it tries to fit into Irssi\'s usage style more than emulating ircII. (23 January 2002)
oopsie.pl	Stops those silly mistakes being sent (spaces at start of ' . 'line, /1/1 for window changes, etc). (09 November 2016)
pastie.pl	Offer to automatically send pastes to a web based paste site (17 September 2007)
remote.pl	Lets you run commands remotely via /msg and a password (20 July 2003)
resize_split.pl	Resizes a split window when it is made active (see comments in script for details) (08 June 2003)
resize_split_hh2.pl	Resizes a split window when it is made active (see comments in script for details) (23 June 2004)
servercomplete.pl	Tab complete servers and userhosts (irc. -> irc server, user@ -> user@host). Useful for lazy ircops for /squit and so on :) (21 January 2002)
sping.pl	/sping [server] returns lag to server specified by sending a remote PING to the server. (07 February 2002)
tab_stop.pl	This script replaces the evil inverted 'I' with a configurable number of whitespaces (31 December 2002)
title.pl	Display configurable title as XTerm title (22 January 2003)
unicode.pl	Get infomation about unicode characters (09 November 2016)
urlinfo.pl	Print short summaries about URLs from known services that are mentioned on IRC. (Including YouTube, etc.) (09 November 2016)
usercount.pl	Adds a usercount for a channel as a statusbar item (20 January 2004)