If you use Skype a lot and like the idea of having different ringtones for some contacts that you have in there, then you will find Skypeman useful for that task.
There is no save dialog, which means that the changes are automatically saved unless you check the default button again in the program window. You can preview any sound here and stop or pause playback at any time. The application supports a variety of formats including mp3, wav, ogg and flac among others. Simply select the type of communication or status that you want to change the sound for, uncheck the default box on the right of it, and use the folder icon to pick a supported audio file from your system. You can set ringtones depending on the online status or type of conversation (online, offline, call, chat).