I like Pidgin and use it myself. It’s an alternative to Trillian and in my opinion works at least as well.
We Say – We love Pidgin too, its a great IM (instant messaging) client that supports lots of protocols. Pidgin is lightweight, fast and supports advanced features like private messaging via the Off-The-Record plug-in. Great recommendation, thanks Alberto!
Download Pidgin here
Download Off-The-Record plug-in here (securely encrypts IM conversations.)