TalkBack is a freeware plugin for Cerulean Studios Multi-Medium chat client Trillian. It was designed to be as lightweight and flexible as possible. It will read any message sent to a chat window aloud, but has the ability to ignore or replace words, making it easier for the TTS engine to speak jargon such as LOL as "laugh out loud". The ignore feature is helpful in instructing the plugin to ignore things like URLs, which can be a real pain to listen to; unless you enjoy that kind of thing.
The ignore feature incorporates the Boost regular expression library which will let you input regular expressions into the ignore list making it much easier to filter out unwanted words and phrases.
In addition you can attach TTS to any trillian event, define a hotkey to immediately cease speech output; and embed speech tags into your converstations. Through this you can change how your contact hears your voice if they also have the plugin installed.