ICQ (I seek you) has been avalable of the PC platform for a few years and has a massive user base. It wasn't long before it was realsed for the Palm platform. Available from ICQ.com it is quite small, and runs very well. Whilst doing other things, such as downloading e-mail, it runs in the background, and beeps when a new message arrives. The only problem is that you have to set up all your contacts again. Personally, I use this all the time!

ICQ : Link Now supports server based contact list. Very good, although gets a nightmare if you have millions of friends online!

Yahoo Messenger : Link Yahoo Client. Seems to have stopped working at the mo, but looks good.