Google Talk / GMail Chat
I saw a green dot next to Rowan's name in GMail today, and thought I'd try out the Chat/Talk feature. Works quite nicely, all within the browser, and working well in Firefox too.
The thing that I found was the most 'cute' was that when I put a smiley in, it turned it around and animated it - but not into some yellow thing like the MSN Msgr ones, but one that still looked like it had been typed. And if you did something like :-) or :^), it would leave the nose in there too, in the same way that it was typed. :)