I've always liked mIRC. There are decent scripts for it, and it isn't very hard to customize for yourself. I also use Xchat on Debian ... haven't gotten used to it, but it's working great. Plugins aren't very plentiful though.
Oh yeah, hydrairc looks sweet. I might give it out a try. If it wasn't for my huge mIRC log files that have been around for years, I'd might be convince to leave mIRC altogether.