In our company, the most important way to communicate with colleagues is through IRC.
Usually we use xchat as a client application, but because I prefer Mac, I had to find some mac clients.
So, I googled for irc clients and I found some useful applications.
There are several metrics to choose the better one. In my case, the money is a big concern (haha…).
So, I choose this one.
This application provides lots of functionality and also very pretty. It also provides iPhone & iPodTouch version of client. I have neither of those gadget but it will be good for someone else.
Another one I concerned was Linkinus (http://www.linkinus.com/).
It has very fancy interface and works very well.
The problem is that it’s commercial one. So, if you want to use it more than 15 days, you should purchase it (cost is $20).