Yahoo Messenger has been one of the leading instant messaging apps for years. Version 10 introduced a whole host of new features, notably in support for video and image links.
One of the more interesting additions is the video support: When you paste in a video link from YouTube and similar video sites, the link is pasted in--and then the video instantly appears inside the chat. This is a nice touch, though the inline video is pretty tiny and can't be resized. This feature also works with links to photos. Not having to click on a favorite link in order to "see" it in chat is a good thing.
Yahoo Messenger 10 also has robust voice support, called Yahoo Voice. Like most other voice over IP solutions, PC to PC calls are free.
