I've got to admit I'm not a big online chatter. This, despite that I once wrote a novel in which half the dialogue took place through IM windows.
But I have enjoyed the occasional chat with family or friends, especially when I was living oversees and the cost of international calls were much higher. I remember at one cubicle job I had, the server blocked us from using any chat software aside from the intranet version, which was rather useless. Even AOL's online version "“ where no application is required "“ was blocked.
But now there's Meebo, which not only allows you to chat without downloading a thing, but also consolidates all your accounts into one. That means you can be signed into all your AOL screen names, your Yahoo!, your MSN, ICQ, Google, whatever you've got going on there "“ at the same time!
And it works remarkable well, complete with a very nifty sound effect every time someone contacts you. So check it out and spread the word. They also have a chat interface you can put right in your blog, for those with ridiculous amounts of free time on your hands. (That's envy speaking, not redicule.)