Konversation has been my IRC client of choice for at least 3 years now, mainly because I find that xchat and ksirc are too bloated, and both lack integration into the K Desktop Environment.
In the early days there were lots of features missing, but very quickly most gaps were filled and almost. Soon I was not missing any truely essential features. The project had its ups and downs, initially a one man project (Dario Abatianni) the project had a few dry spells before it moved to kde-extragear and gained popularity. After that, more authors contributed to the project, the ongoing result is the big 1.0
Check out 1.0’s Changelog, it’s huge, and finally konversation got a tree-view channel-list. One of those things I had been still missing for some time. Test it, you won’t regret it: Avatar’s linked to kabc addressbook-entries, simple, straight forward interface, …
p.s.: I just saw that dendeigh (my linux desktop) made it on this screenshot, hooray 
p.p.s.: in other news, Amarok 1.4.3 was released – music, good!