ChannelBar by Cameroon
ChannelBar allows you to turn on a window that provides a button for each of your open windows. These may be channels, text windows, DCC chat windows and other types of windows through IPC (full support still pending on this one though). Those windows may then be hidden or shown by command clicking on their buttons, special properties set on a per window/button basis and the buttons provide information about the state of the channels they represent.
URL Sniffer by Cameroon
Gather's URLs from your IRC sessions. Double click to launch a URL and Command-Delete to delete them. Supports dragging from the URL list.
Completion11 by DerekS
Nick completion with the tab key, Half completion, adds ': ' or ' ' when needed, and notification when multiple nicks fit your input.
Color11 by DerekS
Nick coloring (your userlist colors) for your channel and action message (/me), support for IRCII mode and text indenting, and message bolding when a message contains your nickname.
IgnoreSaver by lws
Saves your ignore list and reloads it when ShadowIRC is opened.
Misc CTCP Reply by mcclure111
Lets you set responses for CTCP messages.
NickC by lws
Nick completion.
scanblock by John Bafford
Allows you to scan a block of IPs and list all resolving domain names.
SH-Telnet by mcclure111
"primitive but usable" telnet client.
Tint by lws
Commands, msg logger, auto-away, nick coloring, etc.
Typing Rate by anything
Measures your current typing rate in words per minute and displays it on the Inputline.
Overflow Alert by mcclure111
Alerts you if you try to use an /away or /quit message longer than Undernet's maximum length.
BasketCTCP by Casey Jaymes
BasketCTCP is a #mp3* channel plugin for ShadowIRC that catches all the ctcp offers that mp3 servers put out on the channel. So this is really cool so you get a list of mp3s being offered that is up-to-date and easily accessed.

Send comments or suggestions to batmanppc@haque.net.