libnotify is a advanced notification script that has lots of features, requires notification-daemon and libnotify to work (same requirements as latest XChat versions). libnotify.wav can be placed in $HOME/.xchat2/ for sounds to be played automatically on msgs/events (requires sox). The default setup should work fine for most users, but you can change settings near the top of the file.

optional features:
show notifications even if xchat is focused
play audio on notifications (uses "play" from sox)
show only initial notification per event
log events to a seperate tab
notification when kicked
ignore nick/chanserv/X notices

yasis (yet another system info script) is a full feature sysinfo script, displays tons of statistics, all indivdual or in groups. works in any irc client that supports /exec -o .

output example:
[OS] Gentoo Base System 1.12.11.1 (2.6.27-gentoo up 2 days, 18:20) :: [CPU] 1-AMD Athlon(tm) Processor (1410MHz/256KB/10% load) :: [Memory] 196M of 249M (21% Free) :: [Disk] 46.42G of 55.14G (14% Free) :: [Video] ATI Rage 128 PF/PRO AGP 4x TMDS (1152x864/16 Bit/75Hz) :: [Network] Digital Equipment DECchip 21142/43 (eth0: 3.44G In/1.28G Out)

prints all whois/whowas output to active tab with a better look then default. also the most complete whois addon I've seen, most miss lots of hooks.

whois output example:
--------[ whois s0ulslack ]----------------------------
| host: soul@*.qwest.net
| name: I smell like fruity hydroponic
| channel: #idaho #gentoo
| idle: 0:12:52, signon: Mon Apr 20 14:39:34 2009
| secure: is using a secure connection
| actual host: 75.174.117.99
| server: irc.servercentral.net (Server Central Network)

parses the transmission bittorrent client stats file and displays interesting stats. v1.1 requires the latest client (1.51+) and Time::Duration perl module. older clients can try v1.0.

output example:
[bt] In/Out: 305GB/233GB (14284 Files) :: Seed Time: 96d 20h (137 Sessions)