Available instant messaging clients

Pidgin

Webcam Support - Yes
MSN Full Support - Yes
GTalk Full Support - Yes
Voice Chat - Yes
Protocols Supported - Multiple (GTalk, Msn, Yahoo...)
Send Files - Yes
Receive Files - Yes
Emoticons - Yes
Theme/Skin - Yes
Language Support - Yes
Drag & Drop Support - Yes
Ubuntu Notification Support - Yes
Last Updated (Since this Post) - Version 2.7.11 - March 11, 2011
Found in Ubuntu Repository - Yes (Version 1:2.7.11-1ubuntu2)
Now Playing Support - Yes (With several players like Banshee)
Plugins - Yes
PRO - Very compatible.
CON - Very simple/"old like" to the eye.

Empathy

Webcam Support - Yes
MSN Full Support - Yes (No Webcam, Voice Chat)
GTalk Full Support - Yes (Including Voice Chat, Video Chat to Cellular phones)
Voice Chat - Yes
Protocols Supported - Multiple (GTalk, Msn, Yahoo...)
Send Files - Yes
Receive Files - Yes
Emoticons - Yes
Theme/Skin - Yes (Only Chat)
Language Support - Yes
Drag & Drop Support - Yes
Ubuntu Notification Support - Yes
Last Updated (Since this Post) - Version 3.0.0 - April 4, 2011
Found in Ubuntu Repository - Yes (Version 2.34.0-0ubuntu3)
Now Playing Support - Yes (With extensions)
Plugins - No
PRO - Very compatible. Easy to use. Remote Desktop Shared
CON - No Plugin List, No custom theme.

Emesene

Webcam Support - Yes
MSN Full Support - Yes
GTalk Full Support - No
Voice Chat - No
Protocols Supported - MSN Protocol Only (With Plugins GTalk,Facebook can be used)
Send Files - Yes
Receive Files - Yes
Emoticons - Yes
Theme/Skin - Yes
Language Support - Yes
Drag & Drop Support - Yes
Ubuntu Notification Support - Yes
Last Updated (Since this Post) - Version 2.11.5 - May 30, 2011
Found in Ubuntu Repository - Yes (Version 2.11.4+dfsg-0ubuntu1)
Now Playing Support - Not Yet
Plugins - Yes
PRO - MSN Live Messenger Style, Easy to use/setup, Friendly
CON - No Full Video/Audio Support for all protocols