Having recently terminated my association with anything with the words 'Windows' and 'Live' in the same sentence, I've been enjoying the benefits of bloat-free communication with Google Talk. Its IM and VOIP tools are already second-to-none, yet there are plenty of ways you can improve the way you chat using the client, as outlined in Web Worker Daily's recent collection of tips.
Once you've fiddled around with all the juicy hidden features inside the app itself you might want to try bolting on a third party app to further enhance productivity. Because I have several different GMail accounts, I find Google Talk Polygamy particularly useful. The tiny patch gives you the ability to open multiple sessions of the IM client on your desktop, and is a doddle to use. Another useful tool for anyone with multiple GMail log-ins is MessenPass, which is able to quickly recover lost or forgotten passwords for the service.
In general I find the sound quality excellent when making calls using Google Talk. Sometimes though, this can work to its detriment, as it picks up all sorts of background noises, impairing the conversation as a result. Solicall provides a quick remedy for this, as the program can help you reduce the audibility of things like screaming kids, keyboard tapping or blaring televisions.
If you frequently use Google Talk as a VOIP client for conducting business, or if you simply want to keep a record of your conversations with pals then get HotRecorder installed. The plug-in allows you to record, play and store any voice communication you have on the client, opening up a whole new world of possibilities.