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.plIntelligent akill command (11 June 2006)
chanact2.plAdds 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.plCounts 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.plA command to output content of files in various ways (17 September 2003)
foreach_user.plExtends the /foreach command to have /foreach user (users in a channel). Syntax: /foreach user [hostmask] command. (31 December 2002)
nickcolor.plassign 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.plStops those silly mistakes being sent (spaces at start of ' . 'line, /1/1 for window changes, etc). (12 August 2014)
pastie.plOffer to automatically send pastes to a web based paste site (17 September 2007)
remote.plLets you run commands remotely via /msg and a password (20 July 2003)
resize_split.plResizes a split window when it is made active (see comments in script for details) (08 June 2003)
resize_split_hh2.plResizes a split window when it is made active (see comments in script for details) (23 June 2004)
servercomplete.plTab 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.plThis script replaces the evil inverted 'I' with a configurable number of whitespaces (31 December 2002)
title.plDisplay configurable title as XTerm title (22 January 2003)
unicode.plGet infomation about unicode characters (06 July 2014)
urlinfo.plPrint short summaries about URLs from known services that are mentioned on IRC. (Including YouTube, etc.) (22 May 2015)
usercount.plAdds a usercount for a channel as a statusbar item (20 January 2004)
Scripts without headers and other stuff