Babbel is designed from the ground up to give the user all the control over how the client behaves and functions. Some users like separate windows and a shared inputline, others like an all-in-one-window with userlist and inputline attached. Others might like something in between. Babbel gives you that option! The preferences are extensive but not overwelming. It lets you control pretty much every part of Babbel's behavior and function.
With Babbel you can create unlimited connections (if you want). The only limit is how much RAM you have.
In each connection you can define as many nicknames as you like. Babbel will cycle through these nicks when a nickname is already taken when you connect to the server.
You can also define as many servers in your connection as you like so that when a server is not reachable it will cycle to the next in the list automatically.
Ofcourse you can set auto-execute commands that are triggered right after you connect to a server. Babbel also has a seperate section for BNC use, making it 100% BNC friendly.

Link: http://www.babbelirc.com/

Client, written in XUL and JavaScript for Mozilla web browsers. It is designed to run on any platform on which Mozilla runs, such as Mac OS, Linux, BSD, Microsoft Windows, Solaris, IRIX, BeOS, AIX, HP-UX, and OS/2. It currently supports most features of IRC clients, such as connections to multiple servers, IPv6, SSL and UTF-8. It supports JavaScript as a scripting language. Messages are styled using CSS, which means that the style of the client can be easily changed, including one that places photographs next to the names of users who speak in the channel. Features such as DCC, which allows users to transfer files between each other, are now supported.
You must be using a Mozilla based browser to run ChatZilla.

Link: http://www.mozilla.org/projects/rt-messaging/chatzilla/

Gaim is a multi-protocol instant messaging (IM) client for Linux, BSD, MacOS X, and Windows. It is compatible with AIM and ICQ (Oscar protocol), MSN Messenger, Yahoo!, IRC, Jabber, Gadu-Gadu, SILC, Novell GroupWise Messenger, Lotus Sametime, and Zephyr networks.
Gaim users can log in to multiple accounts on multiple IM networks simultaneously. This means that you can be chatting with friends on AOL Instant Messenger, talking to a friend on Yahoo Messenger, and sitting in an IRC channel all at the same time.
Gaim supports many features of the various networks, such as file transfer, away messages, and typing notification. It also goes beyond that and provides many unique features. A few popular features are Buddy Pounces, which give the ability to notify you, send a message, play a sound, or run a program when a specific buddy goes away, signs online, or returns from idle; and plugins, consisting of text replacement, a buddy ticker, extended message notification, iconify on away, spell checking, tabbed conversations, and more.
Gaim runs on a number of platforms, including Windows, Linux, and Qtopia (Sharp Zaurus and iPaq).
Gaim integrates well with GNOME 2 and KDE 3.1's system tray, as well as Windows's own system tray. This allows you to work with Gaim without requiring the buddy list window to be up at all times.

Link: http://www.pidgin.im/

jIRCii is an Internet Relay Chat client (IRC) for Windows, MacOS X, and Linux. jIRCii provides an irc experience similiar to ircii, hADES, and BitchX with the advantages of a solid user interface. Features include DCC/CTCP support, multiple server connections, IRC over SSL support, tab key nickname completion, and over 75 built-in commands. jIRCii is fully scriptable using sleep, a Perl-like language.

Link: http://jirc.hick.org/

Opera is a cross-platform web browser and Internet suite which handles common internet-related tasks, including visiting web sites, sending and receiving e-mail messages, managing contacts, and online chat. It is proprietary software and closed source. Opera's lightweight mobile web browser Opera Mini, and most current versions of its desktop application are offered free-of-charge.
Opera is developed by Opera Software, based in Oslo, Norway. It runs on a variety of operating systems, including many versions of Microsoft Windows, Mac OS X, Solaris, FreeBSD and Linux systems. It is also used in mobile phones, smartphones, Personal Digital Assistants, game consoles and interactive televisions. Technology from Opera is also licensed by other companies for use in such products as Adobe Creative Suite.

Link: http://www.opera.com/

X-Chat, commonly written XChat or xchat, is one of the most popular IRC clients for Unix-like systems. It is also available for Microsoft Windows and Mac OS X (via an offshoot of the project, called X-Chat Aqua, which keeps in sync with the main development branch and is much more popular than the official version maintained by the Fink project). It has a choice of a tabbed or tree interface, support for multiple servers, and a high level of configurability. Both command line and graphical versions are available, although use of the graphical version far outweighs use of the command line version. It is licensed under the GNU General Public License and uses the GTK+ toolkit for its interface.

Link: http://www.xchat.org/ (Free XChat for windows http://www.silverex.org/ )