zsIRC

"This free (!) IRC client was a BIG surprise for me. [...] much-much better than any other free client out there - and, in many respects, even commercial ones!"

"zsIRC has indeed proved to be a very good surprise: it's so much better than all the other free clients out there. It's not only free but also supports logging, has the best-working history (if you have an external / thumb keyboard and are used to the way how desktop / Unix IRC clients work, you.ll certainly welcome it) and has no visible anomalies, unlike both mIRCy (pixel doubling and non-settable character sizes) and PocketIRC (ClearType)."