first, thanks xcoder for making this thread sticky
and here i go again with a collection of messenger softwares
windows live messenger a very widespread messenger, and no need to talk about it.
Yahoo messenger 8.1 this is the official messenger of Yahoo!, it has many features resembling the msn messenger, and it is also known for the stability and fidelity.
Trillian 3.1 aka the ultimate chat program, lets you talk to your msn, yahoo, aim and icq contacts, it has a lot of options in it and it is very reliable and it worth a try.
AIM 6.0.28 is another popular messenger from America online.
Messenger Plus for windows live messenger A very cool msn extension that has a lot of features and among them: event viewer, custom status, emotion sound, costum font color...