General reply:

What's wrong with xchat? It's a lovely little client that's not filled with clutter that you're not likely to use. It looks great under Linux with nice antialiased fonts.

Re: the suggestion: as nightcrawler said, the nickname margin can be a tad annoying when long nicknames are involved. Perhaps an adjustable nickname truncation function could be implementied for nicks that are stupidly long, so that you don't have to keep adjusting the margin.