Hi i am looking for one and i need one that is not buggy and don't take too much system resources...
Miranda........doesn't even require installation. Can be used onUSB thumb drive.
Miranda IM is great. It is small, compact, light-weight, extensible, customizable, modular, open source, free, multi-protocol Instant Message client.
Low CPU usage, low memory footprint, plugins, etc.
* http://en.wikipedia.org/wiki/Miranda_IM
I use Miranda IM to connect to Jabber via a SSL (secure) connection.