Here are pointers on each of these messengers exposing more technical details about how they encrypt their login password, where it is stored and how we can decrypt it manually to recover the password.
Google Talk - 'Exposing the Google Password Secrets'
Windows Live Messenger - 'Exposing the Password Secrets of MSN/Windows Live Messenger'
MSN Messenger - 'Exposing the Password Secrets of MSN/Windows Live Messenger'
AOL Messenger (AIM) - Password Secrets of AIM
Digsby IM - 'Password Secrets of Digsby IM'
PaltalkScene - Exposing the Password Secrets of PaltalkScene
Trillian - 'Password Secrets of Trillion'
Trillian Astra - 'Password Secrets of Trillion'
Pidgin (Formerly Gaim) - 'Password Secrets of Pidgin / Gaim'
MySpaceIM - 'Password Secrets of MySpace IM'
Miranda - 'Password Secrets of Miranda Messenger'
Beyluxe IM - 'Exposing the Password Secrets of Beyluxe Messenger'
XFire - 'Password Secrets of XFire Game Messenger'