YInformer is a nice free software to see status of all your Yahoo Messenger buddies. Even if your Yahoo Messenger buddies are invisible or in stealth mode, YInformer will show them as online. That is really cool.
YInfomer works by sending specially created packets to target users. On receiving the data back, it analyzes it for online status, and webcam status and lets you know if the Yahoo Messenger users are actually online (even if in invisible mode). It also tells if the users have their webcam in broadcast mode.
To use it, just install it, and use the YInformer shortcut to launch this free software.